#include <bits/stdc++.h>

#define FOR(i,a,b) for (int i = (a); i <= (b); i++)
#define FORD(i,a,b) for (int i = (a); i >= (b); i--)
#define REP(i,b) for (int i = 0; i < (b); i++)
#define PB push_back
using namespace std;

vector<vector<vector<long long>>>D;
vector<vector<int>>V;
	int n,m;

long long prv=1000000007;

void dfs1(int v, int f){
	//cout<<v<<" "<<f<<endl;
	
	//ak vrchol je ofarbeny
	D[v][1][2]=1;
	D[v][1][1]=1;
	D[v][0][0]=1;


	REP(i,V[v].size()){
		int child=V[v][i];
		if(child==f)continue;
		
		//sprav dfs
		dfs1(child,v);
		
			
		
		//dynamika
		FORD(j,n,2){
			FOR(k,0,j){
				if(k<j){
					D[v][j][2]+=(D[child][k][0]*D[v][j-k][2])%prv;
				}
				
				//bez
				D[v][j][0]+=((D[child][k][0]+D[child][k][1])*D[v][j-k][0])%prv;
				
				//s
				if(k<j)
					D[v][j][1]+=((D[child][k][2]+D[child][k][1])*D[v][j-k][1])%prv;
				
				D[v][j][0]%=prv;
				D[v][j][1]%=prv;
				D[v][j][2]%=prv;
				//if(D[v][1][2]==0)
				//	cout<<i<<" "<<j<<" "<<k<<endl;
				
			}
		
		}
		
		
		
		
	}
	D[v][1][1]=0;
		D[v][0][0]=0;

	
	/*
	cout<<"vrchol "<<v<<endl;
	cout<<D[v][1][2]<<endl;
	REP(i,n+1){
		cout<<i<<" poc "<<D[v][i][0]<<" "<<D[v][i][1]<<" "<<D[v][i][2]<<endl;
	}
	* */
	
	
	
	
	
}


int main(){
	
	
	while(cin>>n>>m){
		
		V.clear();
		V.resize(n+7);
		REP(i,n-1){
			int a,b;
			cin>>a>>b;
			V[a].PB(b);
			V[b].PB(a);
		}
		D.clear();
		D.resize(n+7,vector<vector<long long>>(n+7,vector<long long>(3,0)));
		
		dfs1(1,-1);
		
		cout<<(D[1][m][0]+D[1][m][1])%prv<<endl;
		
		
		
		
		
	}
	
	
	
	
}