#define _USE_MATH_DEFINES
#include <algorithm>
#include <cstdio>
#include <functional>
#include <iostream>
#include <cfloat>
#include <climits>
#include <cstring>
#include <cmath>
#include <fstream>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <time.h>
#include <vector>
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> i_i;
typedef pair<ll, int> ll_i;
typedef pair<double, int> d_i;
typedef pair<ll, ll> ll_ll;
typedef pair<double, double> d_d;
struct edge { int u, v; ll w; };

int INF = INT_MAX / 10;
ll MOD = 1000000007;
ll _MOD = 1000000009;
double EPS = 1e-10;

void f(int u, int p, vector<vector<int> >& G, vector<vector<int> >& a) {
	a[u] = vector<int>(2, 0);
	a[u][1] = 1;
	for (int i = 0; i < G[u].size(); i++) {
		int v = G[u][i];
		if (v == p) continue;
		f(v, u, G, a);
		int n = a[u].size(), m = a[v].size();
		vector<int> b(min(2001, n + m - 1));
		for (int x = 0; x < n; x++)
			for (int y = 0; y < m; y++)
				if (x + y <= 2000)
					b[x + y] = (b[x + y] + (ll)a[u][x] * a[v][y]) % MOD;
		a[u] = b;
	}
	a[u][0] = (a[u][0] + 1) % MOD;
}

int main() {
	int N, K; cin >> N >> K;
	vector<vector<int> > G(N);
	for (int i = 0; i < N - 1; i++) {
		int a, b; cin >> a >> b;
		G[a].push_back(b);
		G[b].push_back(a);
	}
	vector<vector<int> > a(N);
	f(0, -1, G, a);
	cout << a[0][N - K] << endl;
}