#include "bits/stdc++.h"
using namespace std;
#define FOR(i,j,k) for(int (i)=(j);(i)<(int)(k);++(i))
#define rep(i,j) FOR(i,0,j)
#define each(x,y) for(auto &(x):(y))
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define debug(x) cout<<#x<<": "<<(x)<<endl
#define smax(x,y) (x)=max((x),(y))
#define smin(x,y) (x)=min((x),(y))
#define MEM(x,y) memset((x),(y),sizeof (x))
#define sz(x) (int)(x).size()
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<ll> vll;

template<int MOD>
class ModInt{
public:
    ModInt():value(0){}
    ModInt(long long val):value((int)(val<0?MOD+val%MOD:val%MOD)){ }

    ModInt& operator+=(ModInt that){
        value = value+that.value;
        if(value>=MOD)value-=MOD;
        return *this;
    }
    ModInt& operator-=(ModInt that){
        value -= that.value;
        if(value<0)value+=MOD;
        return *this;
    }
    ModInt& operator*=(ModInt that){
        value = (int)((long long)value * that.value % MOD);
        return *this;
    }
    ModInt &operator/=(ModInt that){
        return *this *= that.inverse();
    }
    ModInt operator+(ModInt that) const{
        return ModInt(*this)+=that;
    }
    ModInt operator-(ModInt that) const{
        return ModInt(*this)-=that;
    }
    ModInt operator*(ModInt that) const{
        return ModInt(*this)*=that;
    }
    ModInt operator/(ModInt that) const {
        return ModInt(*this) /= that;
    }
    ModInt pow(long long k) const{
        if(value == 0)return 0;
        ModInt n = *this, res = 1;
        while(k){
            if(k & 1)res *= n;
            n *= n;
            k >>= 1;
        }
        return res;
    }
    ModInt inverse() const {
        long long a = value, b = MOD, u = 1, v = 0;
        while(b) {
            long long t = a / b;
            a -= t * b;
            swap(a, b);
            u -= t * v;
            swap(u, v);
        }
        return ModInt(u);
    }
    int toi() const{ return value; }

private:
    int value;
};
typedef ModInt<1000000007> mint;
ostream& operator<<(ostream& os, const mint& x){
    os << x.toi();
    return os;
}

int N, K, s[2000];
vi G[2000];
mint dp[2000][2001];

void g(int u, int p){
    s[u] = 1;
    each(v, G[u])if(v != p){
        g(v, u);
        s[u] += s[v];
    }
}

void f(int u, int p){
    dp[u][0] = dp[u][s[u]] = 1;
    each(v, G[u])if(v != p){
        f(v, u);
        for(int i = s[u]-1; i >= 0; --i){
            FOR(j, 1, s[v] + 1){
                if(i + j <= s[u]){
                    dp[u][i+j]+=dp[u][i]*dp[v][j];
                }
            }
        }
    }
}

int main(){
    int u, v;

    cin >> N >> K;
    rep(i, N-1){
        scanf("%d%d", &u, &v);
        G[u].push_back(v);
        G[v].push_back(u);
    }

    g(0, -1);
    f(0, -1);
    cout << dp[0][K] << endl;
}