#include <iostream>
#include <algorithm>
#include <iomanip>
#include <vector>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <tuple>
#include <cmath>
#include <numeric>
#include <functional>
#include <cassert>
#include <atcoder/modint>

#define debug_value(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << #x << "=" << x << endl;
#define debug(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << x << endl;

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

using namespace std;
typedef long long ll;

template<typename T>
vector<vector<T>> vec2d(int n, int m, T v){
    return vector<vector<T>>(n, vector<T>(m, v));
}

template<typename T>
vector<vector<vector<T>>> vec3d(int n, int m, int k, T v){
    return vector<vector<vector<T>>>(n, vector<vector<T>>(m, vector<T>(k, v)));
}

template<typename T>
void print_vector(vector<T> v, char delimiter=' '){
    if(v.empty()) {
        cout << endl;
        return;
    }
    for(int i = 0; i+1 < v.size(); i++) cout << v[i] << delimiter;
    cout << v.back() << endl;
}

using mint = atcoder::modint1000000007;

ostream& operator<<(ostream& os, const mint& m){
    os << m.val();
    return os;
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << setprecision(10) << fixed;
    int n, k; cin >> n >> k;
    vector<vector<int>> g(n);
    for(int i = 0; i < n-1; i++){
        int a, b; cin >> a >> b; a--; b--;
        g[a].push_back(b);
        g[b].push_back(a);
    }
    vector<vector<vector<mint>>> dp(n);
    for(int i = 0; i < n; i++){
        dp[i].assign(g[i].size(), vector<mint>(k));
    }
    function<vector<mint>(int, int)> dfs1 = [&](int v, int par){
        vector<mint> ans(k);
        for(int x = 0; x < k; x++) ans[x] = 1;
        for(int i = 0; i < g[v].size(); i++){
            int to = g[v][i];
            if(to == par) continue;
            dp[v][i] = dfs1(to, v);
            for(int x = 0; x < k; x++){
                ans[x] *= dp[v][i][x];
            }
        }
        for(int x = 1; x < k; x++) ans[x] += ans[x-1];
        // cout << "====" << endl;
        // cout << v << ":"; print_vector(ans);
        return ans;
    };
    auto merge = [&](vector<mint> v, vector<mint> u){
        vector<mint> w(k);
        for(int i = 0; i < k; i++) w[i] = v[i]*u[i];
        return w;
    };
    dfs1(0, -1);
    mint ans = 0;
    function<void(int, int, vector<mint>)> dfs2 = [&](int v, int p, vector<mint> from_par){
        int deg = g[v].size();
        for(int i = 0; i < deg; i++){
            if(g[v][i] == p){
                dp[v][i] = from_par;
                break;
            }
        }
        // cout << "=====" << endl;
        if(v == 0){
            // cout << v << ":";
            for(int x = 0; x < k; x++){
                mint prod = 1;
                for(int i = 0; i < deg; i++){
                    prod *= dp[v][i][x];
                }
                // cout << prod << ' ';
                ans += prod;
            }
            // cout << endl;
        }else{
            // cout << v << ":";
            for(int x = 1; x < k; x++){
                mint prod = 1;
                for(int i = 0; i < deg; i++){
                    if(g[v][i] == p){
                        prod *= dp[v][i][x-1];
                    }else{
                        prod *= dp[v][i][x];
                    }
                }
                // cout << prod << ' ';
                ans += prod;
            }
            // cout << endl;
        }
        auto from_right = vec2d(deg+1, k, mint(0));
        from_right[deg] = vector<mint>(k, mint(1));
        for(int i = deg-1; i >= 0; i--){
            from_right[i] = merge(from_right[i+1], dp[v][i]);
        }
        vector<mint> from_left(k, mint(1));
        for(int i = 0; i < deg; i++){
            int u = g[v][i];
            if(u != p){
                auto x = merge(from_left, from_right[i+1]);
                for(int i = 1; i < k; i++) x[i] += x[i-1];
                dfs2(u, v, x);
            }
            from_left = merge(from_left, dp[v][i]);
        }
    };
    dfs2(0, -1, vector<mint>(k, mint(1)));
    cout << ans << endl;
}