// {{{ Templates
#include <bits/stdc++.h>

#define show(x) cerr << #x << " = " << x << endl

using namespace std;
using ll = long long;
using pii = pair<int, int>;
using vi = vector<int>;

template <typename T>
ostream& operator<<(ostream& os, const vector<T>& v)
{
    os << "sz:" << v.size() << "\n[";
    for (const auto& p : v) {
        os << p << ",";
    }
    os << "]\n";
    return os;
}

template <typename S, typename T>
ostream& operator<<(ostream& os, const pair<S, T>& p)
{
    os << "(" << p.first << "," << p.second
       << ")";
    return os;
}


constexpr ll MOD = (ll)1e9 + 7LL;

template <typename T>
constexpr T INF = numeric_limits<T>::max() / 100;

// }}}

int N;

struct Graph {
    Graph(const int n)
    {
        edge.resize(n);
    }
    void addEdge(const int from, const int to)
    {
        edge[from].push_back(to);
    }
    vector<vector<int>> edge;
};

struct Polynomial {
    Polynomial() : coeff(N + 1, 0), degree(0) {}

    static Polynomial monomial(const ll coe, const int deg)
    {
        Polynomial p;
        p.coeff[deg] = coe;
        p.degree = deg;
        return p;
    }

    Polynomial operator+(const Polynomial& p) const
    {
        Polynomial P;
        if (degree >= p.degree) {
            for (int i = 0; i <= p.degree; i++) {
                P.coeff[i] = (coeff[i] + p.coeff[i]) % MOD;
            }
        } else {
            for (int i = 0; i <= degree; i++) {
                P.coeff[i] = (coeff[i] + p.coeff[i]) % MOD;
            }
            for (int i = degree + 1; i <= p.degree; i++) {
                P.coeff[i] = p.coeff[i];
            }
        }
        P.degree = max(degree, p.degree);
        return (*this);
    }

    Polynomial& operator+=(const Polynomial& p)
    {
        if (degree >= p.degree) {
            for (int i = 0; i <= p.degree; i++) {
                coeff[i] += p.coeff[i];
                coeff[i] = coeff[i] % MOD;
            }
        } else {
            for (int i = 0; i <= degree; i++) {
                coeff[i] += p.coeff[i];
                coeff[i] = coeff[i] % MOD;
            }
            for (int i = degree + 1; i <= p.degree; i++) {
                coeff[i] = p.coeff[i];
                coeff[i] = coeff[i] % MOD;
            }
        }
        degree = max(degree, p.degree);
        return (*this);
    }

    Polynomial operator*(const Polynomial& p) const
    {
        Polynomial P;
        P.degree = degree + p.degree;
        for (int i = 0; i <= P.degree; i++) {
            ll sum = 0;
            for (int j = 0; j <= min(degree, i); j++) {
                sum = (sum + coeff[j] * p.coeff[i - j] % MOD) % MOD;
            }
            P.coeff[i] = sum;
        }
        return P;
    }

    int degree = 0;
    vector<ll> coeff;
};

ostream& operator<<(ostream& os, const Polynomial& p)
{
    for (int i = 0; i <= p.degree; i++) {
        if (i > 0) {
            os << " + ";
        }
        os << p.coeff[i];
        if (i > 0) {
            os << "x^" << i;
        }
    }
    os << endl;
    return os;
}

int size_dfs(const Graph& g, const int s, vector<int>& size)
{
    int num = 1;
    for (const int to : g.edge[s]) {
        num += size_dfs(g, to, size);
    }
    size[s] = num;
    return num;
}

Polynomial dp_dfs(const Graph& g, const int s, const vector<int>& size)
{
    Polynomial P = Polynomial::monomial(1LL, size[s]);
    Polynomial Product = Polynomial::monomial(1LL, 0);
    for (const int to : g.edge[s]) {
        Product = Product * dp_dfs(g, to, size);
    }
    P += Product;
    return P;
}

int main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);

    int K;
    cin >> N >> K;
    Graph g(N);
    for (int i = 0; i < N - 1; i++) {
        int a, b;
        cin >> a >> b;
        g.addEdge(a, b);
    }

    vector<int> size(N, 0);
    size_dfs(g, 0, size);

    cout << dp_dfs(g, 0, size).coeff[K] << endl;

    return 0;
}