#include<bits/stdc++.h>
using namespace std;
using Int = long long;
//INSERT ABOVE HERE
signed main(){
  Int n,k;
  cin>>n>>k;
  vector<vector<Int> > G(n);
  for(Int i=1;i<n;i++){
    Int x,y;
    cin>>x>>y;
    G[x].emplace_back(y);
    G[y].emplace_back(x);
  }
  const Int MOD = 1e9+7;
  vector<vector<Int> > dp(n);
  vector<Int> sz(n,1);
  function<void(Int,Int)> dfs=
    [&](Int v,Int p){
      for(Int u:G[v]){
	if(u==p) continue;
	dfs(u,v);
	sz[v]+=sz[u];
      }
      dp[v].assign(sz[v]+1,0);
      dp[v][0]=1;
      for(Int u:G[v]){
	if(u==p) continue;
	vector<Int> nx(sz[v]+1,0);
	for(Int i=0;i<=sz[v];i++)
	  for(Int j=0;j<=sz[u];j++)
	    if(i+j<=sz[v]) nx[i+j]+=dp[v][i]*dp[u][j]%MOD;
	for(Int i=0;i<=sz[v];i++) nx[i]%=MOD;
	swap(dp[v],nx);
      }
      dp[v][sz[v]]=1;
    };
  dfs(0,-1);
  cout<<dp[0][k]<<endl;
  return 0;
}