#include <bits/stdc++.h>
using namespace std;
using i64 = long long;
#define rep(i,s,e) for(int (i) = (s);(i) <= (e);(i)++)
#define all(x) x.begin(),x.end()

#define int long long

int N,K;

vector<int> G[101010];

const i64 MOD = 1e9 + 7;

vector<int> dfs(int v,int f = -1){
  vector<int> res;
  res.push_back(1);
  for(int to : G[v]){
    if(to == f) continue;
    vector<int> ret = dfs(to,v);
    vector<int> next(res.size() + ret.size() - 1,0);
    for(int i = 0;i < res.size();i++){
      for(int j = 0;j < ret.size();j++){
        (next[i + j] += res[i] * ret[j] % MOD) %= MOD;
      }
    }
    res = next;
  }
  res.push_back(1);
  return res;
}

signed main(){
  cin >> N >> K;
  for(int i = 0;i < N - 1;i++){
    int a,b;
    cin >> a >> b;
    G[a].push_back(b);
    G[b].push_back(a);
  }
  cout << dfs(0)[K] % MOD << endl;
}