#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) {
  dp[crr][0] = 1;
  for (int nxt : grh[crr]) if (nxt != prt) {
    dfs(nxt, crr);
    for (int i = dsc[crr]; i >= 0; i--) {
      for (int j = 1; j <= dsc[nxt]; j++) {
        add(dp[crr][i + j], mul(dp[crr][i], dp[nxt][j]));
      }
    }
    dsc[crr] += dsc[nxt];
  }
  dsc[crr]++;
  dp[crr][dsc[crr]] = 1;
}
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, 0));
  dsc.resize(n, 0);
  dfs(0, 0);
  cout << dp[0][k] << '\n';
  return 0;
}