#include<iostream>
#include<fstream>
#include<sstream>
#include<string>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<ctime>
#include<stack>
#include<queue>
#include<set>
#include<map>
#include<vector>
#include<list>
#include<algorithm>
#include<utility>
#include<complex>
#include<functional>
using namespace std;

#define LL long long
const LL MOD = 1000000007;
int nodesize[2001];
vector<list<int>> child(2001);
LL pt[2001] = { 1 };
LL pc[2001][2001];
LL par[2001];
int K;
int dfs(int v){
	for (int &u : child[v])nodesize[v]+=dfs(u);
	return (++nodesize[v]);
}
void dfs2(int v){
	for (int i = K; i >= nodesize[v]; i--){
		pt[i] = (MOD+pt[i] + pt[i - nodesize[v]] - pc[par[v]][i - nodesize[v]]) % MOD;
		pc[v][i] = (pc[par[v]][i] + pt[i - nodesize[v]] - pc[par[v]][i - nodesize[v]])%MOD;
	}
	for (int &u : child[v])dfs2(u);
	return;
}

int main(void){
	int N;
	int a, b;
	cin >> N>>K;
	for (int i = 1; i < N; i++){
		cin >> a >> b;
		child[a].push_back(b);
		par[b] = a;
	}
	dfs(0);
	dfs2(0);
	cout << pt[K] << endl;

	return(0);
}