// Enjoy your stay.

#include <bits/stdc++.h>

#define long long long
#define LOOPVAR_TYPE long

#define all(x) (x).begin(), (x).end()
#define sz(x) ((LOOPVAR_TYPE)(x).size())
#define foreach(it, X) for(__typeof((X).begin()) it = (X).begin(); it != (X).end(); it++)
#define GET_MACRO(_1, _2, _3, NAME, ...) NAME
#define _rep(i, n) _rep2(i, 0, n)
#define _rep2(i, a, b) for(LOOPVAR_TYPE i = (LOOPVAR_TYPE)(a); i < (LOOPVAR_TYPE)(b); i++)
#define rep(...) GET_MACRO(__VA_ARGS__, _rep2, _rep)(__VA_ARGS__)

#define fir first
#define sec second
#define mp make_pair
#define mt make_tuple
#define pb push_back

const double EPS = 1e-9;
const double PI = acos(-1.0);
const long INF = 1070000000LL;
const long MOD = 1000000007LL;

using namespace std;

typedef istringstream iss;
typedef stringstream sst;
typedef pair<LOOPVAR_TYPE, LOOPVAR_TYPE> pi;
typedef vector<LOOPVAR_TYPE> vi;

const int MN = 2010;

int N, K;
vi g[MN];

vi f(int cur, int pre){
	vi res(1, 1);
	for(int ch: g[cur]){
		if(ch == pre) continue;
		vi sub = f(ch, cur);
		int n = sz(res) - 1;
		int m = sz(sub) - 1;
		vi nres(n + m + 1);
		rep(i, n+1){
			rep(j, m+1){
				nres[i + j] = (nres[i + j] + res[i] * sub[j]) % MOD;
			}
		}
		res = nres;
	}
	res.pb(1);
	return res;
}

int main(){
	cin.tie(0);
	ios_base::sync_with_stdio(0);
	
	cin >> N >> K;
	rep(i, N-1){
		int a, b;
		cin >> a >> b;
		g[a].pb(b);
		g[b].pb(a);
	}
	cout << f(0, -1)[K] << endl;
}