#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for(int i = 0; i < (n); ++i)
#define all(x) (x).begin(),(x).end()
#define ln '\n'
constexpr long long MOD = 1000000007LL;
//constexpr long long MOD = 998244353LL;
typedef long long ll;
typedef unsigned long long ull; 
typedef pair<int, int> pii;
typedef pair<long long, long long> pll;
template<class T, class U> inline bool chmax(T &a, U b) { if (a < b) { a = b; return true;} return false; }
template<class T, class U> inline bool chmin(T &a, U b) { if (a > b) { a = b; return true;} return false; }
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////


template <std::uint_fast64_t Modulus> 
struct ModInt {
    using u64 = std::uint_fast64_t;

    u64 a;

    constexpr ModInt(const long long x = 0) noexcept : a(x >= 0 ? x % Modulus : (Modulus - (-x) % Modulus) % Modulus) {}
    constexpr u64 &value() noexcept { return a; }
    constexpr const u64 &value() const noexcept { return a; }
    constexpr ModInt operator+(const ModInt rhs) const noexcept {return ModInt(*this) += rhs;}
    constexpr ModInt operator-(const ModInt rhs) const noexcept {return ModInt(*this) -= rhs;}
    constexpr ModInt operator*(const ModInt rhs) const noexcept {return ModInt(*this) *= rhs;}
    constexpr ModInt operator/(const ModInt rhs) const noexcept {return ModInt(*this) /= rhs;}
    constexpr ModInt &operator+=(const ModInt rhs) noexcept {
        a += rhs.a;
        if (a >= Modulus) {
            a -= Modulus;
        }
        return *this;
    }
    constexpr ModInt &operator-=(const ModInt rhs) noexcept {
        if (a < rhs.a) {
            a += Modulus;
        }
        a -= rhs.a;
        return *this;
    }
    constexpr ModInt &operator*=(const ModInt rhs) noexcept {
        a = a * rhs.a % Modulus;
        return *this;
    }
    constexpr ModInt &operator/=(ModInt rhs) noexcept {
        u64 exp = Modulus - 2;
        while (exp) {
            if (exp % 2) {
                *this *= rhs;
            }
            rhs *= rhs;
            exp /= 2;
        }
        return *this;
    }

    bool operator==(const ModInt &p) const {return a == p.a;}
    bool operator!=(const ModInt &p) const {return a != p.a;}

    ModInt pow(long long N) const {
        ModInt ret(1), mul(a);
        while(N > 0) {
            if(N & 1) ret *= mul;
            mul *= mul;
            N >>= 1;
        }
        return ret;
    }
};

using mint = ModInt<MOD>;

mint ans[2020][2020];
vector<int> G[2020];
int sub[2020];

void dfs(int v, int pv) {
    vector<mint> arr(2020);
    int sz = 1;
    arr[0] = 1;
    for (auto nv : G[v]) {
        if (nv==pv) continue;
        vector<mint> dp2(2020);
        dfs(nv,v);
        rep(i,sz) {
            rep(j,sub[nv]+1) {
                dp2[i+j] += arr[i]*ans[nv][j];
            }
        }
        swap(arr,dp2);
        sz += sub[nv];
    }
    sub[v] = sz;
    rep(i,sub[v]) ans[v][i] = arr[i];
    ans[v][sub[v]] = 1;
    return;
}
int main() {
    ios::sync_with_stdio(false); cin.tie(nullptr);
    int N,K; cin >> N >> K;
    rep(i,N-1) {
        int u,v; cin >> u >> v;
        G[u].emplace_back(v);
        G[v].emplace_back(u);
    }

    dfs(0,-1);
    cout << ans[0][K].a << ln;
}