#include<bits/stdc++.h>
using namespace std;
#define rep(i,a,b) for(int i=a;i<b;i++)




int mod = 1000000007;
int add(int x, int y) { return (x += y) >= mod ? x - mod : x; }
template<class... T> int add(int x, T... y) { return add(x, add(y...)); }
int mul(int x, int y) { return 1LL * x * y % mod; }
template<class... T> int mul(int x, T... y) { return mul(x, mul(y...)); }
int sub(int x, int y) { return add(x, mod - y); }
int modpow(int a, long long b) { int ret = 1; while (b > 0) { if (b & 1) ret = 1LL * ret * a % mod; a = 1LL * a * a % mod; b >>= 1; } return ret; }
int modinv(int a) { return modpow(a, mod - 2); }
//-----------------------------------------------------------------------------------
int N, K;
vector<int> E[2010];
//-----------------------------------------------------------------------------------
int cnt[2010]; map<int,int> dp[2010];
void merge(int cu, int to) { // dp[cu] = dp[cu] + dp[to]
    map<int, int> cnt;
    for (auto p : dp[cu]) for (auto q : dp[to]) {
        cnt[p.first + q.first] = add(cnt[p.first + q.first], mul(p.second, q.second));
    }
    dp[cu] = cnt;
}
void dfs(int cu, int pa = -1) {
    dp[cu][0] = 1;

    cnt[cu] = 1;
    for (int to : E[cu]) if (pa != to) {
        dfs(to, cu);
        cnt[cu] += cnt[to];

        merge(cu, to);
    }

    dp[cu][cnt[cu]] = 1;
}
//-----------------------------------------------------------------------------------
int main() {
    cin >> N >> K;
    rep(i, 0, N - 1) {
        int a, b; scanf("%d%d", &a, &b);
        E[a].push_back(b); E[b].push_back(a);
    }

    dfs(0);
    printf("%d\n", dp[0][K]);
}