#include <bits/stdc++.h>
#define EPS 1e-9
#define INF 1070000000LL
#define MOD 1000000007LL
#define fir first
#define foreach(it,X) for(auto it=(X).begin();it!=(X).end();it++)
#define numa(x,a) for(auto x: a)
#define ite iterator
#define mp make_pair
#define rep(i,n) rep2(i,0,n)
#define rep2(i,m,n) for(int i=m;i<(n);i++)
#define pb push_back
#define pf push_front
#define sec second
#define sz(x) ((int)(x).size())
#define ALL( c ) (c).begin(), (c).end()
#define gcd(a,b) __gcd(a,b)
#define mem(x,n) memset(x,n,sizeof(x))
#define endl "\n"
using namespace std;
template <int POS, class TUPLE> void deploy(std::ostream &os, const TUPLE &tuple){}
template <int POS, class TUPLE, class H, class ...Ts> void deploy(std::ostream &os, const TUPLE &t){ os << (POS == 0 ? "" : ", ") << get<POS>(t); deploy<POS + 1, TUPLE, Ts...>(os, t); }
template <class T,class U> std::ostream& operator<<(std::ostream &os, std::pair<T,U> &p){ os << "(" << p.first <<", " << p.second <<")";return os; }
template <class T> std::ostream& operator<<(std::ostream &os, std::vector<T> &v){ int remain = v.size(); os << "{"; for(auto e: v) os << e << (--remain == 0 ? "}" : ", "); return os; }
template <class T> std::ostream& operator<<(std::ostream &os, std::set<T> &v){ int remain = v.size(); os << "{"; for(auto e: v) os << e << (--remain == 0 ? "}" : ", "); return os; }
template <class T, class K> std::ostream& operator<<(std::ostream &os, std::map<T, K> &mp){ int remain = mp.size(); os << "{"; for(auto e: mp) os << "(" << e.first << " -> " << e.second << ")" << (--remain == 0 ? "}" : ", "); return os; }
#define DEBUG1(var0) { std::cerr << (#var0) << "=" << (var0) << endl; }
#define DEBUG2(var0, var1) { std::cerr << (#var0) << "=" << (var0) << ", ";DEBUG1(var1); }
#define DEBUG3(var0, var1, var2) { std::cerr << (#var0) << "=" << (var0) << ", ";DEBUG2(var1,var2); }
#define DEBUG4(var0, var1, var2, var3) { std::cerr << (#var0) << "=" << (var0) << ", ";DEBUG3(var1,var2,var3); }
using ll = long long;

vector <int> edge[2010];
int cnt[2010];
int N,K;

vector <ll> go(int now, int par = -1) {
  if (sz(edge[now]) == 1 && par != -1) {
    vector <ll> ret(K+1,0);
    cnt[now] = 1;
    ret[0] = 1;
    ret[1] = 1;
    return ret;
  }
  vector <ll> ret[2];
  ret[0].resize(K+1,0);
  ret[1].resize(K+1,0);
  ret[1][0] = 1;
  int cur = 0, bef = 1;
  int all = 1;
  numa(x,edge[now]) {
    if (x == par) {
      continue;
    }
    auto child = go(x,now);
    all += cnt[x];
    for (int i = 0; i <= K; i++) {
      ret[cur][i] = 0;
    }
    for (int i = 0; i <= K; i++) {
      if (child[i]) {
        for (int j = 0; j + i <= K; j++) {
          ret[cur][i+j] += (child[i] * ret[bef][j] % MOD);
          ret[cur][i+j] %= MOD;
        }
      }
    }
    swap(cur, bef);
  }
  if (K >= all) {
    ret[bef][all] = 1;
  }
  cnt[now] = all;
  //DEBUG2(now, ret[bef]);
  return ret[bef];
}


int main()
{
  cin.tie(0);
  ios_base::sync_with_stdio(0);
  cin >> N >> K;
  rep(i,N-1){
    int x,y;
    cin >> x >> y;
    edge[x].pb(y);
    edge[y].pb(x);
  }
  auto ans = go(0);
  //DEBUG1(ans);
  cout << ans[K] << endl;
  return 0;
}