#include <bits/stdc++.h>
using namespace std;
const int md = 1e9 + 7;
inline void add(int &a, int b) {
  a += b;
  if (a >= md) a -= md;
}
inline int mul(int a, int b) {
  return (int)((long long)a * b % md);
}
vector<vector<int>> grh, dp;
vector<int> dsc;
void dfs (int crr, int prt) {
  for (int nxt : grh[crr]) {
    if (nxt != prt) {
      dfs(nxt, crr);
      vector<int> tmp(dsc[crr] + dsc[nxt] + 1, 0);
      for (int i = dsc[crr]; i >= 0; i--) {
        for (int j = 0; j <= dsc[nxt]; j++) {
          int &crrv = tmp[i + j];
          add(crrv, mul(dp[crr][i], dp[nxt][j]));
        }
      }
      for (int i = 0; i <= dsc[crr] + dsc[nxt]; i++) {
        dp[crr][i] = tmp[i];
      }
      dsc[crr] += dsc[nxt];
    }
  }
  dsc[crr]++;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n, k;
  cin >> n >> k;
  grh.resize(n);
  for (int i = 0; i < n - 1; i++) {
    int a, b;
    cin >> a >> b;
    grh[a].push_back(b);
    grh[b].push_back(a);
  }
  dp.resize(n, vector<int>(n + 1, 1));
  dsc.resize(n, 0);
  dfs(0, 0);
  cout << dp[0][k] << '\n';
  return 0;
}