#include <bits/stdc++.h>
#define GET_MACRO(a, b, c, NAME, ...) NAME
#define rep(...) GET_MACRO(__VA_ARGS__, rep3, rep2)(__VA_ARGS__)
#define rep2(i, a) rep3 (i, 0, a)
#define rep3(i, a, b) for (int i = (a); i < (b); i++)
#define repr(...) GET_MACRO(__VA_ARGS__, repr3, repr2)(__VA_ARGS__)
#define repr2(i, a) repr3 (i, 0, a)
#define repr3(i, a, b) for (int i = (b) - 1; i >= (a); i--)
#define chmin(a, b) ((b) < a && (a = (b), true))
#define chmax(a, b) (a < (b) && (a = (b), true))
using namespace std;
typedef long long ll;

vector<int> G[2020];
ll dp[2020][2020];
int size[2020];
const ll mod = 1e9 + 7;

int dfs2(int curr, int prev) {
	size[curr] = 1;
	for (int next : G[curr]) if (next != prev) {
		size[curr] += dfs2(next, curr);
	}
	return size[curr];
}

void dfs(int curr, int prev) {
	dp[curr][0] = 1;
	dp[curr][size[curr]] = 1;
	for (int next : G[curr]) if (next != prev) {
		dfs(next, curr);
		repr (i, size[curr]) if (dp[curr][i] > 0) rep (j, 1, size[next] + 1) {
			
				(dp[curr][i + j] += dp[curr][i] * dp[next][j]) %= mod;
		}
	}
}

int main() {
	int N, K;
	cin >> N >> K;
	rep (i, N - 1) {
		int u, v;
		cin >> u >> v;
		G[u].push_back(v);
		G[v].push_back(u);
	}
	dfs2(0, -1);
	dfs(0, -1);
	cout << dp[0][K] << endl;
	return 0;
}