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

template<int MOD>
class mod_int {
	unsigned x;
public:
	mod_int() : x(0) { }
	mod_int(int sig) { int sigt = sig % MOD; if (sigt < 0) sigt += MOD; x = sigt; }
	mod_int(long long sig) { int sigt = sig % MOD; if (sigt < 0) sigt += MOD; x = sigt; }
	int get() const { return (int)x; }

	mod_int &operator+=(mod_int that) { if ((x += that.x) >= MOD) x -= MOD; return *this; }
	mod_int &operator-=(mod_int that) { if ((x += MOD - that.x) >= MOD) x -= MOD; return *this; }
	mod_int &operator*=(mod_int that) { x = (unsigned long long)x * that.x % MOD; return *this; }
	mod_int &operator/=(mod_int that) { return *this *= that.inverse(); }

	mod_int operator+(mod_int that) const { return mod_int(*this) += that; }
	mod_int operator-(mod_int that) const { return mod_int(*this) -= that; }
	mod_int operator*(mod_int that) const { return mod_int(*this) *= that; }
	mod_int operator/(mod_int that) const { return mod_int(*this) /= that; }

	bool operator==(const mod_int& that) const { return x == that.x; }

	mod_int inverse() const {
		long long a = x, b = MOD, u = 1, v = 0;
		while (b) {
			long long t = a / b;
			a -= t * b; swap(a, b);
			u -= t * v; swap(u, v);
		}
		return mod_int(u);
	}
};

const int mod = 1e9 + 7;
using mint = mod_int<mod>;

const int MAX = 2000;

vector<int> G[MAX];

int size[MAX];
mint dp[MAX][MAX + 1];
mint tmp[MAX + 1];

void dfs(int v, int prev) {
	size[v] = 0;
	dp[v][0] = 1;
	for (auto to : G[v]) if (to != prev) {
		dfs(to, v);
		for (int j = 0; j <= size[v]; j++) {
			tmp[j] = dp[v][j];
			dp[v][j] = 0;
		}
		for (int j = size[v]; j >= 0; j--) {
			for (int k = 0; k <= size[to]; k++) {
				dp[v][j + k] += tmp[j] * dp[to][k];
			}
		}
		size[v] += size[to];
	}
	size[v] += 1;
	dp[v][size[v]] += 1;
}

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