#include <bits/stdc++.h>
using namespace std;
#define repd(i,a,b) for (ll i=(a);i<(b);i++)
#define rep(i,n) repd(i,0,n)
#define all(x) (x).begin(),(x).end()
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; }
typedef long long ll;
typedef pair<ll,ll> P;
typedef vector<ll> vec;
typedef vector<vec> Graph;
const long long INF = 1LL<<60;
const long long MOD = 1000000007;

// auto mod int
// https://youtu.be/L8grWxBlIZ4?t=9858
// https://youtu.be/ERZuLAxZffQ?t=4807 : optimize
// https://youtu.be/8uowVvQ_-Mo?t=1329 : division
const int mod = MOD;
struct mint {
  ll x; // typedef long long ll;
  mint(ll 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 { return mint(*this) += a;}
  mint operator-(const mint a) const { return mint(*this) -= a;}
  mint operator*(const mint a) const { return mint(*this) *= a;}
  mint pow(ll t) const {
    if (!t) return 1;
    mint a = pow(t>>1);
    a *= a;
    if (t&1) a *= *this;
    return a;
  }

  // for prime mod
  mint inv() const { return pow(mod-2);}
  mint& operator/=(const mint a) { return *this *= a.inv();}
  mint operator/(const mint a) const { return mint(*this) /= a;}
};
istream& operator>>(istream& is, mint& a) { return is >> a.x;}
ostream& operator<<(ostream& os, const mint& a) { return os << a.x;}

// combination mod prime
// https://www.youtube.com/watch?v=8uowVvQ_-Mo&feature=youtu.be&t=1619
struct combination {
  vector<mint> fact, ifact;
  combination(int n):fact(n+1),ifact(n+1) {
    assert(n < mod);
    fact[0] = 1;
    for (int i = 1; i <= n; ++i) fact[i] = fact[i-1]*i;
    ifact[n] = fact[n].inv();
    for (int i = n; i >= 1; --i) ifact[i-1] = ifact[i]*i;
  }
  mint operator()(int n, int k) {
    if (k < 0 || k > n) return 0;
    return fact[n]*ifact[k]*ifact[n-k];
  }
  mint p(int n,int k){
      return fact[n]*ifact[n-k];
  }
} c(1000005);

int main()
{  
    ios::sync_with_stdio(false);
    cin.tie(0);
    ll n,k;
    cin>>n>>k;
    Graph g(n);
    rep(i,n-1){
      ll a,b;
      cin>>a>>b;
      g[a].push_back(b);
      g[b].push_back(a);
    }
    function<vector<mint>(ll,ll)> dfs=[&](ll x,ll p){
      vector<mint> res={1};
      for(ll nx:g[x]){
        if(nx==p)continue;
        vector<mint> v=dfs(nx,x);
        ll c1=res.size();
        ll c2=v.size();
        vector<mint> nxt(c1+c2-1);
        rep(i,res.size())rep(j,v.size()){
          mint now=res[i]*v[j];
          nxt[i+j]+=now;
        }
        swap(nxt,res);
      }
      res.push_back(1);
      return res;
    };
    vector<mint> ans=dfs(0,-1);
    cout<<ans[k]<<endl;
    return 0;
}