#include <bits/stdc++.h>
#include <atcoder/modint>
using mint = atcoder::modint1000000007;
using namespace std;
using ll = long long;

mint ans;
int k0;

struct Graph {
    struct Sub {
        Sub() : x(k0, 1) {}
        Sub &operator+=(const Sub &s) {
            for (int k = 0; k < k0; k++) {
                x[k] *= s.x[k];
            }
            return *this;
        }
        Sub &add_root() {
            for (int k = 1; k < k0; k++) {
                x[k] += x[k - 1];
            }
            return *this;
        }
        vector<mint> x;
    };
    struct Vertex { int n; Sub s; };
    struct Edge { int i, n, r; Sub s; };
    Graph(int n, int m) : v(n, { -1, {} }), e(m), r(m), n(n), m(0) {}
    void add_edge(int i, int j) {
        e[m] = { j, v[i].n, 0, {} };
        v[i].n = m;
        m++;
    }
    Sub dfs0(int i, int p) {
        Sub s;
        for (int j = v[i].n; j >= 0; j = e[j].n) {
            Edge& o = e[j];
            if (o.i == p) continue;

            s += o.s = dfs0(o.i, i);
        }
        return s.add_root();
    }
    void dfs1(int i, int p, Sub *r, Sub s0) {
        int l = 0;
        for (int j = v[i].n; j >= 0; j = e[j].n) {
            Edge& o = e[j];
            if (o.i == p) o.s = s0;
            r[l++] = o.s;
        }
        for (int k = l - 1; k > 0; k--) {
            r[k - 1] += r[k];
        }
        v[i].s = r[0].add_root();

        Sub s;
        int k = 0;
        for (int j = v[i].n; j >= 0; j = e[j].n) {
            Edge& o = e[j];
            k++;
            if (o.i != p) {
                Sub t = s;
                if (k < l) t += r[k];
                dfs1(o.i, i, r + l, t.add_root());
            }
            s += o.s;
        }
    }
    void solve() {
        dfs0(0, -1);
        dfs1(0, -1, &r[0], {});

        ans = 0;
        dfs(0, -1);
        cout << ans.val() << endl;
    }
    void dfs(int i, int p) {
        Sub s, t;
        for (int j = v[i].n; j >= 0; j = e[j].n) {
            Edge& o = e[j];
            if (o.i == p) {
                t = o.s;
                continue;
            }
            s += o.s;
            dfs(o.i, i);
        }
        if (p >= 0) {
            for (int k = 1; k < k0; k++) {
                ans += s.x[k] * t.x[k - 1];
            }
        } else {
            for (int k = 0; k < k0; k++) {
                ans += s.x[k];
            }
        }
    }
    vector<Vertex> v;
    vector<Edge> e;
    vector<Sub> r;
    int n, m;
};

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

    int n;
    cin >> n >> k0;

    Graph g(n, (n - 1) * 2);
    for (int i = 0; i < n - 1; i++) {
        int a, b;
        cin >> a >> b;
        a--; b--;

        g.add_edge(a, b);
        g.add_edge(b, a);
    }
    g.solve();

    return 0;
}