#include <bits/stdc++.h>
using namespace std;
#define repl(i, l, r) for (int i = (l); i < (int)(r); ++i)
#define rep(i, n) repl(i, 0, n)
#define CST(x) cout << fixed << setprecision(x)
#define all(x) (x).begin(), (x).end()
#define sz(x) (int)(x).size()
using ll = long long;
constexpr ll MOD = 1e9 + 7;
constexpr int inf = 1e9 + 10;
constexpr ll INF = (ll)4e18 + 10;
constexpr int dx[9] = {1, 0, -1, 0, 1, -1, -1, 1, 0};
constexpr int dy[9] = {0, 1, 0, -1, 1, 1, -1, -1, 0};
const double PI = acos(-1);
template <typename T>
using MaxHeap = priority_queue<T>;
template <typename T>
using MinHeap = priority_queue<T, vector<T>, greater<T>>;
template <typename T>
inline bool chmax(T &a, T b) {
    return ((a < b) ? (a = b, true) : (false));
}
template <typename T>
inline bool chmin(T &a, T b) {
    return ((a > b) ? (a = b, true) : (false));
}
template <typename T>
inline void yn(const T &a) {
    ((a) ? (cout << "Yes" << endl) : (cout << "No" << endl));
}
template <typename T>
inline void YN(const T &a) {
    ((a) ? (cout << "YES" << endl) : (cout << "NO" << endl));
}
int main() {
    cin.tie(nullptr);
    cout.tie(nullptr);
    ios::sync_with_stdio(false);

    int n, k;
    cin >> n >> k;

    vector<vector<int>> G(n);
    rep(i, n - 1) {
        int a, b;
        cin >> a >> b;
        G[a].emplace_back(b), G[b].emplace_back(a);
    }

    vector<vector<ll>> dp(n);

    auto f = [&G, &dp](auto self, const auto &v, const auto &p) -> int {
        int res = 1;
        dp[v].assign(res + 1, 0);
        dp[v][0] = 1;
        for (const auto &to : G[v]) {
            if (to == p) continue;
            res += self(self, to, v);
        }
        for (const auto &to : G[v]) {
            if (to == p) continue;
            vector<ll> merged(sz(dp[v]) + sz(dp[to]) - 1);
            rep(i, sz(dp[v])) rep(j, sz(dp[to])) {
                merged[i + j] += dp[v][i] * dp[to][j] % MOD;
                merged[i + j] %= MOD;
            }
            dp[v] = merged;
        }
        dp[v][res] = 1;
        return res;
    };

    f(f, 0, -1);

    cout << dp[0][k] << endl;

    return 0;
}