#include<bits/stdc++.h>
using namespace std;
#define rep(i,n) for(ll i=0;i<n;i++)
#define repl(i,l,r) for(ll i=(l);i<(r);i++)
#define per(i,n) for(ll i=(n)-1;i>=0;i--)
#define perl(i,r,l) for(ll i=r-1;i>=l;i--)
#define fi first
#define se second
#define pb push_back
#define ins insert
#define pqueue(x) priority_queue<x,vector<x>,greater<x>>
#define all(x) (x).begin(),(x).end()
#define CST(x) cout<<fixed<<setprecision(x)
#define vtpl(x,y,z) vector<tuple<x,y,z>>
#define rev(x) reverse(x);
using ll=long long;
using vl=vector<ll>;
using vvl=vector<vector<ll>>;
using pl=pair<ll,ll>;
using vpl=vector<pl>;
using vvpl=vector<vpl>;
const ll MOD=1000000007;
const ll MOD9=998244353;
const int inf=1e9+10;
const ll INF=4e18;
const ll dy[9]={0,1,-1,0,1,1,-1,-1,0};
const ll dx[9]={1,0,0,-1,1,-1,1,-1,0};
template<class T> inline bool chmin(T& a, T b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}
template<class T> inline bool chmax(T& a, T b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}
vl conv(vl a,vl b){
    vl ret(a.size()+b.size()-1);
    rep(i,a.size()){
        rep(j,b.size()){
            ret[i+j]+=a[i]*b[j];
            ret[i+j]%=MOD;
        }
    }
    return ret;
}
vvl g(2010);
vvl dp(2010);
void dfs(ll v,ll par=-1){
    for(auto p:g[v]){
        if(p==par)continue;
        dfs(p,v);
    }
    dp[v]={1};
    for(auto p:g[v]){
        if(p==par)continue;
        dp[v]=conv(dp[v],dp[p]);
    }
    dp[v].push_back(1);
}
int main(){
    ll n,k;cin >> n >>k;
    rep(i,n-1){
        ll a,b;cin >> a >> b;
        g[a].pb(b);g[b].pb(a);
    }
    dfs(0);
    cout << dp[0][k] <<endl;
}