#include <bits/stdc++.h>
#define M_PI       3.14159265358979323846   // pi

using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll, ll> P;
typedef tuple<ll, ll, ll> t3;
typedef tuple<ll, ll, ll, ll> t4;
typedef tuple<ll, ll, ll, ll, ll> t5;

#define rep(a,n) for(ll a = 0;a < n;a++)

template<typename T>
static inline void chmin(T& ref, const T  value) {
	if (ref > value) ref = value;
}

template<typename T>
static inline void chmax(T& ref, const T value) {
	if (ref < value) ref = value;
}

#include <atcoder/all>
using namespace atcoder;
typedef modint1000000007 mint;


int main() {
	int n, k;
	cin >> n >> k;
	vector<vector<int>> g(n);
	rep(i, n - 1) {
		int a, b;
		cin >> a >> b;
		g[a].push_back(b);
		g[b].push_back(a);
	}
	vector<int> cs(n, 0);
	function<int(int, int)> dfs = [&](int current, int parent) {
		int c = 1;
		for (auto x : g[current]) {
			if (x == parent) continue;
			c += dfs(x, current);
		}
		cs[current] = c;
		return c;
	};
	dfs(0, -1);
	vector<mint> dp2(k + 1, 0);
	dp2[k] = 1;
	function<void(int, int, vector<mint>&)> dfs2 = [&](int current, int parent, vector<mint>& dp) {
		//塗らないパターン
		vector<mint> temp = dp;
		//子供を個別に塗り分けていくパターン
		for (auto x : g[current]) {
			if (x == parent) continue;
			dfs2(x, current, temp);
		}
		//自分以下をすべて塗るパターン
		for (int x = cs[current]; x <= k; x++) {
			temp[x - cs[current]] += dp[x];
		}
		dp = temp;
	};
	dfs2(0, -1, dp2);
	cout << dp2[0].val() << endl;
	return 0;
}