#include <bits/stdc++.h>

#ifdef LOCAL
#include "dump.hpp"
#else
#define dump(...)
#endif

using namespace std;

#define REP(i, a, b) for(int i = (a); i < int(b); ++i)
#define rep(i, n) REP(i, 0, n)
#define ALL(x) begin(x), end(x)

template<class T> inline void chmax(T &a, const T &b) { if(a < b) a = b; }
template<class T> inline void chmin(T &a, const T &b) { if(a > b) a = b; }

typedef vector<vector<int>> graph;

constexpr int mod = 1000000007;
constexpr int MAX = 2000;

int n, k;
vector<int> G[MAX];

pair<int, vector<int>> dfs(int v, int p) {
	int size = 1;
	vector<vector<int>> dp;
	dp.reserve(G[v].size());

	for(const auto &c : G[v]) {
		if(c == p) continue;
		const auto result = dfs(c, v);
		size += result.first;
		dp.emplace_back(move(result.second));
	}

	if(dp.empty()) return make_pair(1, vector<int>{1, 1});

	int max_idx = -1;
	int max_size = 0;
	for(int i = 0; i < dp.size(); ++i) {
		if(max_size < dp[i].size()) {
			max_idx = i;
			max_size = dp[i].size();
		}
	}

	vector<int> res = move(dp[max_idx]);
	const int m = min(size, k);
	res.resize(m + 1, 0);

	for(int i = 0; i < dp.size(); ++i) {
		if(i == max_idx) continue;

		vector<int> tmp(m + 1, 0);
		for(int j = m; j >= 0; --j) {
			for(int l = dp[i].size() - 1; l >= 0; --l) {
				if(j + l > m) continue;
				tmp[j + l] = (tmp[j + l] + static_cast<long long>(res[j]) * dp[i][l]) % mod;
			}
		}
		res = move(tmp);
	}
	if(size <= k) res[size] += 1;

	dump(v, size, res);

	return make_pair(size, res);
}

int main() {
	cin.tie(nullptr);
	ios::sync_with_stdio(false);

	cin >> n >> k;

	for(int i = 0; i < n - 1; ++i) {
		int a, b;
		cin >> a >> b;
		G[a].emplace_back(b);
		G[b].emplace_back(a);
	}

	const auto ans = dfs(0, -1);
	cout << ans.second[k] << endl;

	return EXIT_SUCCESS;
}