#include<bits/stdc++.h>
using namespace std;
#include<atcoder/all>
using namespace atcoder;
vector<vector<modint1000000007>> dp(3030);
vector<vector<int>> g;

void solve(int t, int p){
	if (g[t].size() == 1 && p != -1){
		dp[t] = {1, 1};
	}

	dp[t] = {1};
	for (auto x : g[t]){
		solve(x, t);

		vector<modint1000000007> merge(dp[t].size() + dp[x].size() + 1);
		for (int i = 0; i <= (int)dp[t].size(); i++){
			for (int j = 0; j <= (int)dp[x].size(); j++){
				merge[i + j] = dp[t][i] * dp[t][j];
			}
		}
		dp[t] = merge;
	}
	dp[t].back() = 1;
}

int main(){
	int n, k;
	cin >> n >> k;
	g.resize(n);
	for (int i = 0; i < n - 1; i++){
		int u, v;
		cin >> u >> v;
		u--; v--;
		g[u].push_back(v);
		g[v].push_back(u);
	}
	
	solve(0, -1);
	cout << dp[0][k].val() << endl;
}