#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include <complex>
#include <queue>
#include <set>
#include <map>

using namespace std;

#define REP(i,a,b) for(int i=a;i<(int)b;i++)
#define rep(i,n) REP(i,0,n)

using ll  = long long;
using VLL = vector<ll>;

int constexpr MOD = 1e9+7;
int constexpr Max = 2010;

int N, K;
VLL g[Max];

auto rec(int curr, int parent)
  -> VLL  // 着目している根付き木について、黒く塗られている数->そのパターン数
{
  VLL ret(1, 1);
  for(auto ch: g[curr]) {
    if(ch == parent) { continue; }
    auto subTree = rec(ch, curr);
    auto currK = ret.size() - 1; // 自分を除く
    auto newK = subTree.size() - 1; // 自分を除く
    VLL nret(currK + newK + 1);
    rep(iteCurrK, currK + 1) rep(iteNewK, newK + 1) {
      (nret[iteCurrK + iteNewK] += ret[iteCurrK] * subTree[iteNewK]) %= MOD;
    }
    ret = nret;
  }
  ret.push_back(1);
  return ret;
}

int main() {

  cin >> N >> K;
  rep(i, N-1) {
    int a, b; cin >> a >> b;
    g[a].push_back(b), g[b].push_back(a);
  }

  cout << rec(0, -1)[K] << endl;

  return 0;
}