#include <bits/stdc++.h>
#define fi first
#define se second
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define rrep(i,n) for(int i = 1; i <= (n); ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
#define srep(i,s,t) for (int i = s; i < t; ++i)
#define rng(a) a.begin(),a.end()
#define rrng(a) a.rbegin(),a.rend()
#define maxs(x,y) (x = max(x,y))
#define mins(x,y) (x = min(x,y))
#define isin(x,l,r) ((l) <= (x) && (x) < (r))
#define pb push_back
#define eb emplace_back
#define sz(x) (int)(x).size()
#define pcnt __builtin_popcountll
#define uni(x) x.erase(unique(rng(x)),x.end())
#define snuke srand((unsigned)clock()+(unsigned)time(NULL));
#define show(x) cout<<#x<<" = "<<x<<endl;
#define PQ(T) priority_queue<T,v(T),greater<T> >
#define bn(x) ((1<<x)-1)
#define dup(x,y) (((x)+(y)-1)/(y))
#define newline puts("")
#define v(T) vector<T>
#define vv(T) v(v(T))
using namespace std;
typedef long long int ll;
typedef unsigned uint;
typedef unsigned long long ull;
typedef pair<int,int> P;
typedef tuple<int,int,int> T;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ll> vl;
typedef vector<P> vp;
typedef vector<T> vt;
inline int getInt() { int x; scanf("%d",&x); return x;}
template<typename T>inline istream& operator>>(istream&i,v(T)&v)
{rep(j,sz(v))i>>v[j];return i;}
template<typename T>string join(const v(T)&v)
{stringstream s;rep(i,sz(v))s<<' '<<v[i];return s.str().substr(1);}
template<typename T>inline ostream& operator<<(ostream&o,const v(T)&v)
{if(sz(v))o<<join(v);return o;}
template<typename T1,typename T2>inline istream& operator>>(istream&i,pair<T1,T2>&v)
{return i>>v.fi>>v.se;}
template<typename T1,typename T2>inline ostream& operator<<(ostream&o,const pair<T1,T2>&v)
{return o<<v.fi<<","<<v.se;}
template<typename T>inline ll suma(const v(T)& a) { ll res(0); for (auto&& x : a) res += x; return res;}
const double eps = 1e-10;
const ll LINF = 1001002003004005006ll;
const int INF = 1001001001;
#define dame { puts("-1"); return 0;}
#define yn {puts("Yes");}else{puts("No");}
const int MX = 1005;

// Mod int
const int mod = 1000000007;
// const int mod = 998244353;
struct mint {
  ll x;
  mint():x(0){}
  mint(ll x):x((x%mod+mod)%mod){}
  // mint(ll x):x(x){}
  mint& fix() { x = (x%mod+mod)%mod; return *this;}
  mint operator-() const { return mint(0) - *this;}
  mint& operator+=(const mint& a){ if((x+=a.x)>=mod) x-=mod; return *this;}
  mint& operator-=(const mint& a){ if((x+=mod-a.x)>=mod) x-=mod; return *this;}
  mint& operator*=(const mint& a){ (x*=a.x)%=mod; return *this;}
  mint operator+(const mint& a)const{ return mint(*this) += a;}
  mint operator-(const mint& a)const{ return mint(*this) -= a;}
  mint operator*(const mint& a)const{ return mint(*this) *= a;}
  bool operator<(const mint& a)const{ return x < a.x;}
  bool operator==(const mint& a)const{ return x == a.x;}
};
istream& operator>>(istream&i,mint&a){i>>a.x;return i;}
ostream& operator<<(ostream&o,const mint&a){o<<a.x;return o;}
typedef vector<mint> vm;
//

int n, m;

// Rerooting
// TODO: vertex info, edge info
struct Rerooting {
  struct DP {
    vm dp;
    DP():dp(m,1) {}
    DP& operator+=(const DP& a) {
      rep(i,m) dp[i] *= a.dp[i];
      return *this;
    }
    DP& addRoot() {
      rep(i,m-1) dp[i+1] += dp[i];
      return *this;
    }
    DP operator+(const DP& a) const { return DP(*this) += a;}
  };
  
  int n;
  vvi to;
  vv(DP) dp;
  v(DP) ans;
  mint tot;

  Rerooting(int n=0):n(n),to(n),dp(n),ans(n) {}
  void add(int a, int b) {
    to[a].pb(b);
    to[b].pb(a);
  }
  void init() {
    dfs(0);
    bfs(0);
  }

  DP dfs(int v, int p=-1) {
    DP dpSum;
    dp[v] = v(DP)(sz(to[v]));
    rep(i,sz(to[v])) {
      int u = to[v][i];
      if (u == p) continue;
      dp[v][i] = dfs(u,v);
      dpSum += dp[v][i];
    }
    return dpSum.addRoot();
  }
  void bfs(int v, const DP& dpP=DP(), int p=-1) {
    int deg = sz(to[v]);
    int pi = -1;
    rep(i,deg) if (to[v][i] == p) dp[v][i] = dpP, pi = i;

    v(DP) dpSumL(deg+1);
    rep(i,deg) dpSumL[i+1] = dpSumL[i] + dp[v][i];
    v(DP) dpSumR(deg+1);
    for (int i = deg-1; i >= 0; --i) dpSumR[i] = dpSumR[i+1] + dp[v][i];
    ans[v] = DP(dpSumL[deg]).addRoot();

    DP now;
    if (pi != -1) {
      now = dpSumL[pi]+dpSumR[pi+1];
      now.dp[0] = 0;
      rep(i,m-1) now.dp[i+1] *= dpP.dp[i];
      now.addRoot();
    } else {
      now = ans[v];
    }
    tot += now.dp.back();

    rep(i,deg) {
      int u = to[v][i];
      if (u == p) continue;
      bfs(u, (dpSumL[i] + dpSumR[i+1]).addRoot(), v);
    }
  }
};


int main() {
  cin>>n>>m;
  Rerooting g(n);
  rep(i,n-1) {
    int a,b;
    scanf("%d%d",&a,&b);
    --a; --b;
    g.add(a,b);
  }
  g.init();
  cout<<g.tot<<endl;
  return 0;
}