#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;

ll memo[2010][2010];
ll memo2[2010][2010];
vector <int> edge[2010];
int N,K;
int childs[2010];

int dfs(int now, int par = -1){
  childs[now] = 1;
  numa(x,edge[now]){
    if (x != par) {
      childs[now] += dfs(x,now);
    }
  }
  return childs[now];
}

ll calc(int par, int now, vector <pair <int,int> > &Ks, int K);

ll dp_go(int now, int K, int par = -1){
  //black
  if (childs[now] < K) {
    return 0;
  }
  if (childs[now] == K) {
    return 1;
  }
  if (K == 0) {
    return 1;
  }
  if (memo[now][K] >= 0) {
    return memo[now][K];
  }
  vector <pair <int,int > > Ks;
  numa(x,edge[now]){
    if (x != par) {
      Ks.pb(mp(x, childs[x]));
    }
  }
  ll ret = calc(now, 0, Ks, K);
  return memo[now][K] = ret;
}


ll calc(int par, int now, vector <pair <int,int> > &Ks, int K){
  auto x = Ks[now].fir;
  auto child_max = Ks[now].sec;
  if (now == sz(Ks) - 1) {
    return dp_go(x, K, par);
  }
  if (memo2[x][K] >= 0) {
    return memo2[x][K];
  }
  
  ll ret = 0;
  for (int k = 0; k <= min(K, child_max); k++) {
    auto add = dp_go(x, k, par);
    if (add) {
      add *= calc(par, now + 1, Ks, K - k);
      add %= MOD;
      ret += add;
      ret %= MOD;
    }
  }
  return memo2[x][K] = ret;
}



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);
  }
  mem(memo,-1);
  mem(memo2,-1);
  dfs(0);
  cout << dp_go(0, K) << endl;
  
  return 0;
}