import java.util.ArrayList;
import java.util.Arrays;
import java.util.Scanner;

class Main {
	public static void main(String[] args) {
		new Main().run();
	}
	
	final long MOD=(long)1e9+7;
	
	long ADD(long...a) {
		long ret=0;
		for(long v:a)ret=(ret+v)%MOD;
		return ret;
	}
	
	int pointer=0;
	
	void dfs(int cur,int par,ArrayList<Integer>[] g,int[] l,int[] r,int[] v) {
		l[cur]=pointer;
		v[pointer++]=cur;
		for(int dst:g[cur]) {
			if(dst==par)continue;
			dfs(dst,cur,g,l,r,v);
		}
		r[cur]=pointer;
		v[pointer++]=cur;
	}
	
	void run() {
		Scanner sc=new Scanner(System.in);
		int N=sc.nextInt();
		int[] l=new int[N];
		int[] r=new int[N];
		int[] v=new int[2*N];
		Arrays.fill(l, -1);
		Arrays.fill(r, -1);
		Arrays.fill(v, -1);
		int K=sc.nextInt();
		ArrayList<Integer>[] g=new ArrayList[N];
		for(int i=0;i<N;++i)g[i]=new ArrayList<>();
		for(int i=0;i<N-1;++i) {
			int a=sc.nextInt();
			int b=sc.nextInt();
			g[a].add(b);
			g[b].add(a);
		}
		dfs(0,-1,g,l,r,v);
		long[][] dp=new long[2*N][K+1];
		for(int i=0;i<dp.length;++i) {
			for(int j=0;j<dp[i].length;++j)dp[i][j]=ADD(dp[i][j],i==0?(j==0?1:0):dp[i-1][j]);
			if(r[v[i]]==i)continue;
			int ni=r[v[i]];
			int add=(r[v[i]]-l[v[i]]+1)/2;
			for(int cur=0;cur+add<=K;++cur) {
				int ncur=cur+add;
				dp[ni][ncur]+=(i==0?(cur==0?1:0):dp[i-1][cur]);
				dp[ni][ncur]%=MOD;
			}
		}
		System.out.println(dp[2*N-1][K]);
	}
	
	static void tr(Object... objects) {
		System.out.println(Arrays.deepToString(objects));
	}

}