#include <cstdio>
#include <algorithm>
#include <stack>
#include <queue>
#include <deque>
#include <vector>
#include <string>
#include <string.h>
#include <cstdlib>
#include <ctime>
#include <cmath>
#include <map>
#include <set>
#include <iostream>
#include <sstream>
#include <cctype>
#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 gep(i,g,j) for(int i = g.head[j]; i != -1; i = g.e[i].next)
#define each(it,c) for(__typeof((c).begin()) it=(c).begin();it!=(c).end();it++)
#define rng(a) a.begin(),a.end()
#define maxs(x,y) x = max(x,y)
#define mins(x,y) x = min(x,y)
#define pb push_back
#define sz(x) (int)(x).size()
#define pcnt __builtin_popcount
#define snuke srand((unsigned)clock()+(unsigned)time(NULL));
using namespace std;
typedef long long int ll;
typedef pair<int,int> P;
inline int in() { int x; scanf("%d",&x); return x;}

const int MX = 100005, INF = 1000010000;
const ll LINF = 1000000000000000000ll;
const double eps = 1e-10;
const int di[] = {-1,0,1,0}, dj[] = {0,-1,0,1}; //^<v>

// Mod int
const int mod = 1000000007;
struct mint{
	ll x;
	mint():x(0){}
	mint(ll x):x((x%mod+mod)%mod){}
	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;}
};
//
typedef vector<int> vi;
typedef vector<mint> vm;
typedef vector<vm> vvm;

int n, k;
vi to[MX];

int s[MX];
vvm dp[MX];

void dfs(int v, int p=-1) {
  s[v] = 1;
  dp[v] = vvm(2,vm(2));
  dp[v][0][0] = 1;
  dp[v][1][1] = 1;
  for (int u : to[v]) {
    if (u == p) continue;
    dfs(u,v);
    vvm a = dp[v];
    vvm& b = dp[u];
    rep(i,2) dp[v][i] = vm(s[v]+s[u]+1,0);
    rep(i,s[v]+1)rep(j,s[u]+1) {
      dp[v][0][i+j] += a[0][i]*b[0][j];
      dp[v][0][i+j] += a[0][i]*b[1][j];
      dp[v][1][i+j] += a[1][i]*b[1][j];
    }
    s[v] += s[u];
  }
}

int main(){
  cin >> n >> k;
  rep(i,n-1) {
    int a, b;
    cin >> a >> b;
    to[a].pb(b);
    to[b].pb(a);
  }
  dfs(0);
  mint ans = 0;
  rep(i,2) ans += dp[0][i][k];
  cout << ans.x << endl;
  return 0;
}