#include <cstdio>
#include <vector>
#include <algorithm>
using namespace std;

typedef long long LL;

const LL MOD = 1000000007;

vector<vector<int> > G;
vector<int> vis;

vector<LL> dfs(int u){
	vis[u] = 1;
	vector<LL> x(1, 1LL);
	for(int v : G[u]){
		if(!vis[v]){
			vector<LL> y = dfs(v);
			vector<LL> z(x.size() + y.size() - 1);
			for(size_t i = 0; i < x.size(); ++i){
				for(size_t j = 0; j < y.size(); ++j){
					LL &r = z[i + j];
					r = (r + x[i] * y[j]) % MOD;
				}
			}
			x.swap(z);
		}
	}
	x.push_back(1LL);
	return x;
}

int main(){
	int n, k;
	scanf("%d%d", &n, &k);
	G.resize(n);
	vis.assign(n, 0);
	for(int i = 1; i < n; ++i){
		int a, b;
		scanf("%d%d", &a, &b);
		G[a].push_back(b);
		G[b].push_back(a);
	}
	printf("%lld\n", dfs(0)[k]);
}