#include "bits/stdc++.h"
using namespace std;

vector<int> es[3000];
long long dp[3000][3000];
int child[3000];

long long mod = 1000000007;

int pos[3000];
int rev[3000];

int main() {
	int N, K;
	cin >> N >> K;
	for (int i = 0; i < N - 1; i++)
	{
		int a, b;
		cin >> a >> b;
		es[a].push_back(b);
		es[b].push_back(a);
	}

	queue<int> q;
	q.push(0);
	int cnt = 0;
	for (int i = 0; i < N; i++)
	{
		pos[i] = rev[i] = -1;
	}
	pos[0] = 0;
	rev[0] = 0;
	cnt++;
	while (!q.empty()){
		int now = q.front(); q.pop();
		for (auto i : es[now]){
			if (pos[i] == -1){
				pos[i] = cnt;
				rev[cnt] = i;
				cnt++;
				q.push(i);
			}
		}
	}
	for (int ii = N - 1; ii >= 0; ii--)
	{
		int i = rev[ii];
		child[i] = 1;
		dp[i][0] = 1;
		for (auto j : es[i]){
			if (pos[j] < pos[i]) continue;
			for (int k = child[i] - 1; k >= 0; k--)
			{
				for (int l = child[j]; l >= 1; l--)
				{
					dp[i][k + l] += dp[i][k] * dp[j][l];
					dp[i][k + l] %= mod;
				}
			}
			child[i] += child[j];
		}
		dp[i][child[i]] = 1;
	}


	cout << dp[0][K] % mod << endl;
}