#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint1000000007;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000002

int N,K;
vector<vector<int>> E;
vector<vector<vector<mint>>> dp;

void dfs(int cur,int p){
	dp[cur].resize(2,vector<mint>(2,0));
	dp[cur][0][0] = 1;
	rep(i,E[cur].size()){
		int to = E[cur][i];
		if(to==p)continue;
		dfs(to,cur);
		vector ndp(dp[cur].size()+dp[to].size(),vector<mint>(2,0));
		
		rep(j,dp[cur].size()){
			rep(k,2){
				rep(jj,dp[to].size()){
					rep(kk,2){
						ndp[j+jj][k|kk] += dp[cur][j][k] * dp[to][jj][kk];
					}
				}
			}
		}
		swap(dp[cur],ndp);
	}
	rep(i,dp[cur].size()){
		dp[cur][i][1] += dp[cur][i][0];
	}
	for(int i=dp[cur].size()-1;i>=1;i--){
		dp[cur][i][0] = dp[cur][i-1][0];
	}
	dp[cur][0][0] = 0;
}

int main(){	
	
	cin>>N>>K;
	E.resize(N);
	rep(i,N-1){
		int a,b;
		cin>>a>>b;
		E[a].push_back(b);
		E[b].push_back(a);
	}
	dp.resize(N);
	
	dfs(0,-1);
	
	cout<<(dp[0][K][0] + dp[0][K][1]).val()<<endl;
	
	return 0;
	
}