#include <bits/stdc++.h>
using namespace std;

const long long MOD = 1000000007;

int main() {
  int n, k;
  cin >> n >> k;
  vector<vector<int>> g(n);
  for (int i = 0; i < n - 1; i++) {
    int a, b;
    cin >> a >> b;
    g[a].push_back(b);
    g[b].push_back(a);
  }
  auto merge = [&](const vector<long long> &a, const vector<long long> &b) {
    vector<long long> ret(a.size() + b.size() - 1);
    for (int i = 0; i < a.size(); i++) {
      for (int j = 0; j < b.size(); j++) {
        (ret[i + j] += a[i] * b[j]) %= MOD;
      }
    }
    return ret;
  };
  auto dfs = [&](auto &&dfs, int now, int pre) -> vector<long long> {
    vector<long long> dp(2);
    dp[0] = 1;
    for (int nex : g[now]) {
      if (nex != pre) {
        dp = merge(dp, dfs(dfs, nex, now));
      }
    }
    dp.back() = 1;
    return dp;
  };
  auto dp = dfs(dfs, 0, 0);
  cout << dp[k] % MOD << endl;
}