#include "bits/stdc++.h"
using namespace std;
#define rep(i,n) for(int i=0;i<n;i++)
#define ALL(v) (v).begin(),(v).end()
#define MP(a,b) make_pair(a,b)
typedef long long LL;
typedef pair<int, int> PI;
typedef vector<int> VI;
const LL MOD = 1000000007LL;
vector<int> G[2000];
LL dp[2000][2001];
int tree[2000];
int N, K;
void cnt(int v, int par) {
	tree[v] = 1;
	rep(i, G[v].size()) {
		int to = G[v][i];
		if (to == par) continue;
		cnt(to, v);
		tree[v] += tree[to];
	}
}
void dfs(int v, int par) {
	LL dp2[2][2001] = { 0 };
	int sum = 0;
	int now = 0;
	dp2[now][0] = 1;
	rep(i, G[v].size()) {
		int to = G[v][i];
		if (to == par) continue;
		dfs(to, v);
		for (int j = 0; j <= sum; j++) {
			for (int k = 0; k <= tree[to]; k++) {
				LL t = (dp2[now][j] * dp[to][k]) % MOD;
				if (j + k <= K) (dp2[now^1][j + k] += t) %= MOD;
			}
		}
		for (int j = 0; j <= tree[v]; j++) dp2[now][j] = 0;
		sum += tree[to];
		now ^= 1;
	}
	(dp2[now][tree[v]] += 1) %= MOD;
	for (int i = 0; i <= tree[v]; i++) dp[v][i] = dp2[now][i];
}
int main() {
	cin >> N >> K;
	rep(i, N - 1) {
		int a, b;
		cin >> a >> b;
		G[a].push_back(b);
		G[b].push_back(a);
	}
	cnt(0, -1);
	dfs(0, -1);
	cout << dp[0][K] << endl;

}