#include<bits/stdc++.h>
using namespace std;
using ll = long long;


//const ll mod = 998'244'353;
const ll mod = 1'000'000'007;
//const ll mod = 67'280'421'310'721;
struct mint{
    long long x;
    mint(long long x=0):x((x%mod+mod)%mod){}
    mint operator-() const{
        return mint(-x);
    }
    mint& operator+=(const mint& a){
        if((x+=a.x)>=mod)x-=mod;
        return *this;
    }
    mint& operator-=(const mint& a){
        if((x+=mod-a.x)>=mod)x-=mod;
        return *this;
    }
    mint& operator*=(const  mint& a){
        (x *= a.x) %= mod;
        return *this;
    }
    mint operator+(const mint& a) const{
        mint res(*this);
        return res+=a;
    }
    mint operator-(const mint& a) const{
        mint res(*this);
        return res-=a;
    }
    mint operator*(const mint& a) const{
        mint res(*this);
        return res*=a;
    }
    mint pow(long long n) const {
        assert(0 <= n);
        mint a = *this, r = 1;
        while (n) {
            if (n & 1) r *= a;
            a *= a;
            n >>= 1;
        }
        return r;
    }
    mint inv() const{
        return pow(mod-2);
    }
    mint& operator/=(const mint& a){
        return (*this)*=a.inv();
    }
    mint operator/(const mint& a) const {
        mint res(*this);
        return res/=a;
    }
    friend ostream& operator<<(ostream& os, const mint& m){
        os << m.x;
        return os;
    }
    bool operator==(const mint& a) const {
        return x == a.x;
    }
    bool operator<(const mint& a) const{
        return x < a.x;
    }
};

const int mx = 2100;
int n,k;
vector<int> g[mx];
int sz[mx];

int sdfs(int ni,int p){
    sz[ni] = 1;
    for(auto&to:g[ni]) if(to!=p){
        sz[ni] += sdfs(to,ni);
    }
    return sz[ni];
}


vector<vector<mint> >dfs(int ni,int p){
    vector<vector<mint> >ans(2,vector<mint>(2,0));
    ans[0][0] = 1;
    ans[1][1] = 1;
    for(auto&to:g[ni]) if(to!=p) {
        vector<vector<mint> > nxt(2,vector<mint>(sz[to]+ans[0].size()+1,0));
        vector<vector<mint> > use = dfs(to,ni);
        for(int i = 0;i<ans[0].size();i++){
            for(int j = 0;j<=sz[to];j++){
                if(i+j>sz[ni]) break;
                nxt[0][i+j] += ans[0][i] * ( use[1][j]+use[0][j]);
                nxt[1][i+j] += ans[1][i] * use[1][j];
            }
        }
        swap(ans,nxt);
    }
    return ans;
}


int main(){
    cin>>n>>k;
    for(int i = 0;i<n-1;i++){
        int u,v;
        cin>>u>>v;
        g[u].push_back(v);
        g[v].push_back(u);
    }
    sdfs(0,-1);
    vector<vector<mint> > ans = dfs(0,-1);
    cout<<ans[0][k]+ans[1][k]<<endl;
}