module main;
// https://mayokoex.hatenablog.com/entry/2015/05/03/122625 より
// 木DP、深さ優先探索
import std;

int N, K;
int[][] G;
immutable MOD = 1_000_000_007L;

long[] dfs(int v, int p)
{
	long[] ret = [1L];
	foreach (next; G[v]) {
		if (next == p) continue;
		long[] tmp = dfs(next, v);
		int n = ret.length.to!int;
		int m = tmp.length.to!int;
		auto nret = new long[](n + m - 1);
		foreach (i; 0 .. n) foreach (j; 0 .. m) {
			(nret[i + j] += ret[i] * tmp[j]) %= MOD;
		}
		ret = nret;
	}
	ret ~= 1;
	return ret;
}

void main()
{
	// 入力
	readln.chomp.formattedRead("%d %d", N, K);
	G = new int[][](N);
	foreach (_; 0 .. N - 1) {
		int a, b;
		readln.chomp.formattedRead("%d %d", a, b);
		G[a] ~= b;
		G[b] ~= a;
	}
	// 答えの計算と出力
	writeln(dfs(0, -1)[K]);
}