#include <bits/stdc++.h>
using namespace std;
#if __has_include(<atcoder/all>)
#include <atcoder/all>
using namespace atcoder;
template<int mod>istream &operator>>(istream &is,static_modint<mod> &a){long long b;is>>b;a=b;return is;}
istream &operator>>(istream &is,modint &a){long long b;cin>>b;a=b;return is;}
#endif
using ll=long long;
using ull=unsigned long long;
using P=pair<ll,ll>;
template<typename T>using minque=priority_queue<T,vector<T>,greater<T>>;
template<typename T>bool chmax(T &a,const T &b){return (a<b?(a=b,true):false);}
template<typename T>bool chmin(T &a,const T &b){return (a>b?(a=b,true):false);}
template<typename T1,typename T2>istream &operator>>(istream &is,pair<T1,T2>&p){is>>p.first>>p.second;return is;}
template<typename T>istream &operator>>(istream &is,vector<T> &a){for(auto &i:a)is>>i;return is;}
template<typename T1,typename T2>void operator++(pair<T1,T2>&a,int n){a.first++,a.second++;}
template<typename T1,typename T2>void operator--(pair<T1,T2>&a,int n){a.first--,a.second--;}
template<typename T>void operator++(vector<T>&a,int n){for(auto &i:a)i++;}
template<typename T>void operator--(vector<T>&a,int n){for(auto &i:a)i--;}
#define reps(i,a,n) for(int i=(a);i<(n);i++)
#define rep(i,n) reps(i,0,n)
#define all(x) x.begin(),x.end()
#define pcnt(x) __builtin_popcount(x)
ll myceil(ll a,ll b){return (a+b-1)/b;}
template<typename T,size_t n,size_t id=0>
auto vec(const int (&d)[n],const T &init=T()){
  if constexpr (id<n)return vector(d[id],vec<T,n,id+1>(d,init));
  else return init;
}
#ifdef LOCAL
#include "debug.h"
#else
#define debug(...) static_cast<void>(0)
template<typename T1,typename T2>ostream &operator<<(ostream &os,const pair<T1,T2>&p){os<<p.first<<' '<<p.second;return os;}
#endif
void SOLVE();
int main(){
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  #ifdef LOCAL
  clock_t start=clock();
  #endif
  int testcase=1;
  //cin>>testcase;
  for(int i=0;i<testcase;i++){
    SOLVE();
  }
  #ifdef LOCAL
  cout<<"time:";
  cout<<(clock()-start)/1000;
  cout<<"ms\n";
  #endif
}
int n,k;
vector<vector<int>>to;
using mint=modint1000000007;
vector<vector<mint>>dp,ep;
void dfs(int x,int p){
  dp[x]={1,0};
  ep[x]={0,1};
  for(auto i:to[x])if(i!=p){
    dfs(i,x);
    vector<mint>nxtdp(dp[x].size()+dp[i].size()-1,0),nxtep(ep[x].size()+ep[i].size()-1,0);
    rep(j,dp[x].size())rep(k,dp[i].size()){
      nxtdp[j+k]+=dp[x][j]*(dp[i][k]+ep[i][k]);
      nxtep[j+k]+=ep[x][j]*ep[i][k];
    }
    swap(dp[x],nxtdp),swap(ep[x],nxtep);
  }
}
void SOLVE(){
  cin>>n>>k;
  to.resize(n);
  rep(i,n-1){
    int u,v;
    cin>>u>>v;
    to[u].emplace_back(v);
    to[v].emplace_back(u);
  }
  dp.resize(n);
  ep.resize(n);
  dfs(0,-1);
  cout<<(dp[0][k]+ep[0][k]).val()<<endl;
}