#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const ll mod=1000000007;
#define rep(i,n) for(int i=0;i<n;i++)
vector<int> G[2000];bool used[2000];
int k;
vector<ll> dp[2000];
void merge(int i,int j){
  int l1=dp[i].size();
  int l2=dp[j].size();
  vector<ll> nex;nex.resize(l1+l2-1,0);
  rep(i1,l1){
   rep(i2,l2){
    nex[i1+i2]+=dp[i][i1]*dp[j][i2]%mod;
    nex[i1+i2]%=mod;
   }
  }
  dp[i]=nex;
}
void dfs(int id){
 used[id]=true;dp[0].resize(1,1);ll sum=1;
 rep(j,G[id].size()){
  int to=G[id][j];
  if(used[to])continue;
  dfs(to);merge(id,to);
  int len=dp[to].size();
  sum=sum*dp[to][len-1]%mod;
 }
 int len=dp[id].size();
 dp[id][len-1]+=sum;dp[id][len-1]%=mod;
}
int main(){
  int n;cin>>n>>k;
  rep(i,n-1){
    int a,b;cin>>a>>b;
    G[a].push_back(b);
    G[b].push_back(a);
  }
 dfs(0);
 cout<<dp[0][k]<<endl;
}