#include <bits/stdc++.h>
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define chmax(a, b) a = max(a, b)
#define chmin(a, b) a = min(a, b)
#define all(x) (x).begin(), (x).end()
using namespace std;
using ll = long long;
using P = pair<int,int>;
using VI = vector<int>;
using VVI = vector<VI>;

#define MOD 1000000007
//#define MOD 998244353
struct mint {
	int i;
	mint() : i(0) {}
	mint(int x) {
		i = int(x % MOD);
		if (i < 0) i += MOD;
	}
	template<class T> mint(T x) {
		i = int(x % MOD);
		if (i < 0) i += MOD;
	}
	mint operator+(const mint x) const {return i + x.i;}
	mint operator-(const mint x) const {return i - x.i;}
	mint operator*(const mint x) const {return (long long)i * x.i;}
	mint operator/(const mint x) const {return (long long)i * x.pow(MOD - 2).i;}
	mint inv() {return pow(MOD - 2);}
	template<class T> mint pow(T p) const {
		long long r = 1;
		long long t = i;
		for(; p > 0; p >>= 1) {
			if (p & 1) r = r * t % MOD;
			t = t * t % MOD;
		}
		return r;
	}
	template<class T1, class T2> static mint pow(T1 a, T2 b) {
		long long r = 1;
		long long t = (long long)(a % MOD);
		for(; b > 0; b >>= 1) {
			if (b & 1) r = r * t % MOD;
			t = t * t % MOD;
		}
		return r;
	}
	mint& operator+=(const mint x) {
		i = (i + x.i) % MOD;
		return *this;
	}
	mint& operator-=(const mint x) {
		i = i - x.i;
		if (i < 0) i += MOD;
		return *this;
	}
	mint& operator*=(const mint x) {
		i = (int)((long long)i * x.i % MOD);
		return *this;
	}
	mint& operator/=(const mint x) {
		i = (long long)i * x.pow(MOD - 2).i % MOD;
		return *this;
	}
};

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



VVI to;
int n, c;

vector<mint> dfs(int u, int p=-1) {
    vector<mint> dp(c + 1);
    vector<vector<mint>> cdp;
    for(int v: to[u]) {
        if (v == p) continue;
        cdp.push_back(dfs(v, u));
    }
    for(int i = 1; i <= c; i++) {
        mint t = 1;
        for(auto& d: cdp) {
            mint acc = 0;
            if (i - 3 >= 1) acc += d[i-3];
            if (i + 3 <= c) acc += d[i+3];
            t *= acc;
        }
        dp[i] = t;
    }
    return dp;
}

int main() {
    cin >> n >> c;
    to.resize(n);
    rep(i, n-1) {
        int a, b;
        cin >> a >> b;
        a--; b--;
        to[a].push_back(b);
        to[b].push_back(a);
    }
    auto a = dfs(0);
    mint ans = 0;
    for(int i = 1; i <= c; i++) {
        ans += a[i];
    }
    cout << ans << endl;
}