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

typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef long long LL;
typedef pair<LL, LL> PLL;

#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define EB emplace_back
#define MP make_pair
#define SZ(a) int((a).size())
#define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())

#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)

#define FF first
#define SS second
template<class S, class T>
istream& operator>>(istream& is, pair<S,T>& p){
  return is >> p.FF >> p.SS;
}

const double EPS = 1e-10;
const double PI  = acos(-1.0);
const LL MOD = 1e9+7;

int N, K;
VI chd[2000];
LL dp[2000][2010];
int sz[2000];
void dfs(int u, int p){
  sz[u] = 1;
  for(int c: chd[u]){
	if(c == p) continue;
	dfs(c,u);
	sz[u] += sz[c];
  }
  
  if(sz[u] <= K){
	dp[u][sz[u]] = 1;
  }

  int crt = 0, nxt = 1;
  vector<LL> tmp[2];
  tmp[crt] = vector<LL>(1,1);
  for(int c: chd[u]){
	if(c == p) continue;
	int n = SZ(tmp[crt]), m = sz[c];
	tmp[nxt].assign(n+m, 0);
	REP(i,n) REP(j,m+1){
	  tmp[nxt][i+j] += tmp[crt][i] * dp[c][j];
	  tmp[nxt][i+j] %= MOD;
	}
	swap(crt, nxt);
  }

  for(int i=0;i<min(K+1,SZ(tmp[crt]));++i){
	dp[u][i] += tmp[crt][i];
	dp[u][i] %= MOD;
  }
}

int main(){
  cin.tie(0);
  ios_base::sync_with_stdio(false);

  cin >> N >> K;
  REP(i,N-1){
	int a, b; cin >> a >> b;
	chd[a].PB(b);
	chd[b].PB(a);
  }

  dfs(0,-1);
  cout << dp[0][K] << endl;

  return 0;
}