#include<bits/stdc++.h>
using namespace std;
const int mod = 1000000007;

int N, K;
vector< int > graph[2000];
int dp[2000][2001];
int size[2000]; // SubTreeSize

int dfs(int idx, int prev)
{
  size[idx] = 1;
  for(int i = 0; i < graph[idx].size(); i++) {
    if(graph[idx][i] == prev) continue;
    size[idx] += dfs(graph[idx][i], idx);
  }
  return(size[idx]);
}


int rec(int idx, int prev, int mul)
{
  if(~dp[idx][mul]) return(dp[idx][mul]);
  int* dp2 = dp[idx];
  for(int i = 0; i <= K; i++) dp2[i] = 0;
  dp2[0] = 1;
  for(int i = 0; i < graph[idx].size(); i++) {
    if(graph[idx][i] == prev) continue;
    for(int j = K - 1; j >= 0; j--) {
      if(dp2[j] == 0) continue;
      for(int k = K - j; k > 0; k--) {
        (dp2[j + k] += dp2[j] * rec(graph[idx][i], idx, k)) %= mod;
      }
    }
  }
  (dp2[size[idx]] += 1) %= mod;
  return(dp2[mul]);
}

int main()
{ 
  fill_n(*dp, 2000 * 2001, -1);

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