#pragma GCC optimize ("Ofast")
#include<bits/stdc++.h>
using namespace std;
#define MD (1000000007U)
void *wmem;
char memarr[96000000];
template<class T> inline void walloc1d(T **arr, int x, void **mem = &wmem){
  static int skip[16] = {0, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1};
  (*mem) = (void*)( ((char*)(*mem)) + skip[((unsigned long long)(*mem)) & 15] );
  (*arr)=(T*)(*mem);
  (*mem)=((*arr)+x);
}
struct Modint{
  unsigned val;
  Modint(){
    val=0;
  }
  Modint(int a){
    val = ord(a);
  }
  Modint(unsigned a){
    val = ord(a);
  }
  Modint(long long a){
    val = ord(a);
  }
  Modint(unsigned long long a){
    val = ord(a);
  }
  inline unsigned ord(unsigned a){
    return a%MD;
  }
  inline unsigned ord(int a){
    a %= (int)MD;
    if(a < 0){
      a += MD;
    }
    return a;
  }
  inline unsigned ord(unsigned long long a){
    return a%MD;
  }
  inline unsigned ord(long long a){
    a %= (int)MD;
    if(a < 0){
      a += MD;
    }
    return a;
  }
  inline unsigned get(){
    return val;
  }
  inline Modint &operator+=(Modint a){
    val += a.val;
    if(val >= MD){
      val -= MD;
    }
    return *this;
  }
  inline Modint &operator-=(Modint a){
    if(val < a.val){
      val = val + MD - a.val;
    }
    else{
      val -= a.val;
    }
    return *this;
  }
  inline Modint &operator*=(Modint a){
    val = ((unsigned long long)val*a.val)%MD;
    return *this;
  }
  inline Modint &operator/=(Modint a){
    return *this *= a.inverse();
  }
  inline Modint operator+(Modint a){
    return Modint(*this)+=a;
  }
  inline Modint operator-(Modint a){
    return Modint(*this)-=a;
  }
  inline Modint operator*(Modint a){
    return Modint(*this)*=a;
  }
  inline Modint operator/(Modint a){
    return Modint(*this)/=a;
  }
  inline Modint operator+(int a){
    return Modint(*this)+=Modint(a);
  }
  inline Modint operator-(int a){
    return Modint(*this)-=Modint(a);
  }
  inline Modint operator*(int a){
    return Modint(*this)*=Modint(a);
  }
  inline Modint operator/(int a){
    return Modint(*this)/=Modint(a);
  }
  inline Modint operator+(long long a){
    return Modint(*this)+=Modint(a);
  }
  inline Modint operator-(long long a){
    return Modint(*this)-=Modint(a);
  }
  inline Modint operator*(long long a){
    return Modint(*this)*=Modint(a);
  }
  inline Modint operator/(long long a){
    return Modint(*this)/=Modint(a);
  }
  inline Modint operator-(void){
    Modint res;
    if(val){
      res.val=MD-val;
    }
    else{
      res.val=0;
    }
    return res;
  }
  inline operator bool(void){
    return val!=0;
  }
  inline operator int(void){
    return get();
  }
  inline operator long long(void){
    return get();
  }
  inline Modint inverse(){
    int a = val;
    int b = MD;
    int u = 1;
    int v = 0;
    int t;
    Modint res;
    while(b){
      t = a / b;
      a -= t * b;
      swap(a, b);
      u -= t * v;
      swap(u, v);
    }
    if(u < 0){
      u += MD;
    }
    res.val = u;
    return res;
  }
  inline Modint pw(unsigned long long b){
    Modint a(*this);
    Modint res;
    res.val = 1;
    while(b){
      if(b&1){
        res *= a;
      }
      b >>= 1;
      a *= a;
    }
    return res;
  }
  inline bool operator==(int a){
    return ord(a)==val;
  }
  inline bool operator!=(int a){
    return ord(a)!=val;
  }
}
;
inline Modint operator+(int a, Modint b){
  return Modint(a)+=b;
}
inline Modint operator-(int a, Modint b){
  return Modint(a)-=b;
}
inline Modint operator*(int a, Modint b){
  return Modint(a)*=b;
}
inline Modint operator/(int a, Modint b){
  return Modint(a)/=b;
}
inline Modint operator+(long long a, Modint b){
  return Modint(a)+=b;
}
inline Modint operator-(long long a, Modint b){
  return Modint(a)-=b;
}
inline Modint operator*(long long a, Modint b){
  return Modint(a)*=b;
}
inline Modint operator/(long long a, Modint b){
  return Modint(a)/=b;
}
inline int my_getchar_unlocked(){
  static char buf[1048576];
  static int s = 1048576;
  static int e = 1048576;
  if(s == e && e == 1048576){
    e = fread_unlocked(buf, 1, 1048576, stdin);
    s = 0;
  }
  if(s == e){
    return EOF;
  }
  return buf[s++];
}
inline void rd(int &x){
  int k;
  int m=0;
  x=0;
  for(;;){
    k = my_getchar_unlocked();
    if(k=='-'){
      m=1;
      break;
    }
    if('0'<=k&&k<='9'){
      x=k-'0';
      break;
    }
  }
  for(;;){
    k = my_getchar_unlocked();
    if(k<'0'||k>'9'){
      break;
    }
    x=x*10+k-'0';
  }
  if(m){
    x=-x;
  }
}
struct MY_WRITER{
  char buf[1048576];
  int s;
  int e;
  MY_WRITER(){
    s = 0;
    e = 1048576;
  }
  ~MY_WRITER(){
    if(s){
      fwrite_unlocked(buf, 1, s, stdout);
    }
  }
}
;
MY_WRITER MY_WRITER_VAR;
void my_putchar_unlocked(int a){
  if(MY_WRITER_VAR.s == MY_WRITER_VAR.e){
    fwrite_unlocked(MY_WRITER_VAR.buf, 1, MY_WRITER_VAR.s, stdout);
    MY_WRITER_VAR.s = 0;
  }
  MY_WRITER_VAR.buf[MY_WRITER_VAR.s++] = a;
}
inline void wt_L(char a){
  my_putchar_unlocked(a);
}
inline void wt_L(int x){
  int s=0;
  int m=0;
  char f[10];
  if(x<0){
    m=1;
    x=-x;
  }
  while(x){
    f[s++]=x%10;
    x/=10;
  }
  if(!s){
    f[s++]=0;
  }
  if(m){
    my_putchar_unlocked('-');
  }
  while(s--){
    my_putchar_unlocked(f[s]+'0');
  }
}
inline void wt_L(Modint x){
  int i;
  i = (int)x;
  wt_L(i);
}
struct graph{
  int N;
  int *es;
  int **edge;
  void setEdge(int N__, int M, int A[], int B[], void **mem = &wmem){
    int i;
    N = N__;
    walloc1d(&es, N, mem);
    walloc1d(&edge, N, mem);
    for(i=(0);i<(N);i++){
      es[i] = 0;
    }
    for(i=(0);i<(M);i++){
      es[A[i]]++;
      es[B[i]]++;
    }
    for(i=(0);i<(N);i++){
      walloc1d(&edge[i], es[i], mem);
    }
    for(i=(0);i<(N);i++){
      es[i] = 0;
    }
    for(i=(0);i<(M);i++){
      edge[A[i]][es[A[i]]++] = B[i];
      edge[B[i]][es[B[i]]++] = A[i];
    }
  }
  void getDist(int root, int res[], void *mem = wmem){
    int i;
    int j;
    int k;
    int*q;
    int s;
    int z;
    walloc1d(&q, N, &mem);
    for(i=(0);i<(N);i++){
      res[i]=-1;
    }
    res[root]=0;
    s=0;
    z=1;
    q[0]=root;
    while(z){
      i=q[s++];
      z--;
      for(j=(0);j<(es[i]);j++){
        k=edge[i][j];
        if(res[k]>=0){
          continue;
        }
        res[k]=res[i]+1;
        q[s+z++]=k;
      }
    }
  }
}
;
int N;
int K;
int A[1000];
int B[1000];
graph g;
Modint res;
int up[1000];
int d[1000];
int vis[1000][1000];
Modint dp[1000][1000];
Modint solve(int n, int k){
  int Lj4PdHRW;
  Modint res = 1;
  if(k<0){
    return 0;
  }
  if(vis[n][k]){
    return dp[n][k];
  }
  vis[n][k] = 1;
  for(Lj4PdHRW=(0);Lj4PdHRW<(g.es[n]);Lj4PdHRW++){
    auto &i = g.edge[n][Lj4PdHRW];
    if(i==up[n]){
      continue;
    }
    res *= solve(i,k);
  }
  res += solve(n,k-1);
  return dp[n][k] = res;
}
Modint dp2[1000][1000];
void dfs(int n){
  int xr20shxY;
  if(up[n]==-1){
    dp2[n][0] = 1;
    res += dp[n][K-1];
  }
  else{
    int i;
    Modint s = 0;
    Modint t;
    for(i=(0);i<(K);i++){
      if(i){
        t = dp[up[n]][i] -dp[up[n]][i-1];
      }
      else{
        t = dp[up[n]][i] -0;
      }
      t /= dp[n][i];
      s += dp2[up[n]][i];
      dp2[n][i] = t * s;
    }
    s = 0;
    for(i=(1);i<(K);i++){
      s += dp2[n][i-1];
      res += (dp[n][i]-dp[n][i-1]) * s;
    }
  }
  for(xr20shxY=(0);xr20shxY<(g.es[n]);xr20shxY++){
    auto &i = g.edge[n][xr20shxY];
    if(i==up[n]){
      continue;
    }
    dfs(i);
  }
}
int main(){
  int i;
  wmem = memarr;
  rd(N);
  rd(K);
  {
    int KrdatlYV;
    for(KrdatlYV=(0);KrdatlYV<(N-1);KrdatlYV++){
      rd(A[KrdatlYV]);A[KrdatlYV] += (-1);
      rd(B[KrdatlYV]);B[KrdatlYV] += (-1);
    }
  }
  g.setEdge(N,N-1,A,B);
  g.getDist(0, d);
  up[0] = -1;
  for(i=(0);i<(N);i++){
    int V9aVTaxx;
    for(V9aVTaxx=(0);V9aVTaxx<(g.es[i]);V9aVTaxx++){
      auto &j = g.edge[i][V9aVTaxx];
      if(d[j]==d[i]-1){
        up[i] = j;
      }
    }
  }
  solve(0, K-1);
  dfs(0);
  wt_L(res);
  wt_L('\n');
  return 0;
}
// cLay varsion 20200509-1

// --- original code ---
// int N, K, A[1000], B[1000];
// graph g;
// Modint res;
// 
// int up[1000], d[1000];
// int vis[1000][1000];
// Modint dp[1000][1000];
// Modint solve(int n, int k){
//   Modint res = 1;
//   if(k<0) return 0;
//   if(vis[n][k]) return dp[n][k];
//   vis[n][k] = 1;
//   rep[g.edge[n]](i,g.es[n]){
//     if(i==up[n]) continue;
//     res *= solve(i,k);
//   }
//   res += solve(n,k-1);
//   return dp[n][k] = res;
// }
// 
// Modint dp2[1000][1000];
// void dfs(int n){
//   if(up[n]==-1){
//     dp2[n][0] = 1;
//     res += dp[n][K-1];
//   } else {
//     Modint s = 0, t;
//     rep(i,K){
//       t = dp[up[n]][i] - if[i, dp[up[n]][i-1], 0];
//       t /= dp[n][i];
//       s += dp2[up[n]][i];
//       dp2[n][i] = t * s;
//     }
//     s = 0;
//     rep(i,1,K){
//       s += dp2[n][i-1];
//       res += (dp[n][i]-dp[n][i-1]) * s;
//     }
//   }
// 
//   // wt("---",n,res);
//   // wt(dp[n](K));
//   // wt(dp2[n](K));
// 
//   rep[g.edge[n]](i,g.es[n]){
//     if(i==up[n]) continue;
//     dfs(i);
//   }
// }
// 
// {
//   rd(N,K,(A--,B--)(N-1));
//   g.setEdge(N,N-1,A,B);
// 
//   g.getDist(0, d);
//   up[0] = -1;
//   rep(i,N) rep[g.edge[i]](j,g.es[i]) if(d[j]==d[i]-1) up[i] = j;
// 
//   solve(0, K-1);
//   dfs(0);
// 
//   wt(res);
// }