import java.io.*; import java.util.*; class Main { static final long MOD=1000000007; static ArrayList<Integer>[]g; static int k; static long[][][]dp; static void mul(long[]x,long[]y,int xl,int yl){ long[]r=new long[k+1]; for(int i=0;i<=xl;++i){ for(int j=0;j<=Math.min(k-i,yl);++j){ r[i+j]=(r[i+j]+x[i]*y[j])%MOD; } } System.arraycopy(r,0,x,0,k+1); } static int dfs(int v,int p){ int c=1; dp[0][v][0]=1; if(k>=1)dp[1][v][1]=1; long[]tmp=new long[k+1]; for(int w:g[v]){ if(p==w)continue; int sub=dfs(w,v); mul(dp[1][v],dp[1][w],c,sub); for(int j=0;j<=k;++j)tmp[j]=(dp[0][w][j]+dp[1][w][j])%MOD; mul(dp[0][v],tmp,c,sub); c+=sub; } return c; } @SuppressWarnings("unchecked") public static void main(String[] args) { MyScanner sc = new MyScanner(); out = new PrintWriter(new BufferedOutputStream(System.out)); int n=sc.nextInt(); k=sc.nextInt(); g=new ArrayList[n]; Arrays.setAll(g,x->new ArrayList<Integer>()); for(int i=0;i<n-1;++i){ int a=sc.nextInt(); int b=sc.nextInt(); g[a].add(b); g[b].add(a); } dp=new long[2][n][k+1]; dfs(0,-1); //System.err.println(Arrays.deepToString(dp)); out.println((dp[0][0][k]+dp[1][0][k])%MOD); out.close(); } // http://codeforces.com/blog/entry/7018 //-----------PrintWriter for faster output--------------------------------- public static PrintWriter out; //-----------MyScanner class for faster input---------- public static class MyScanner { BufferedReader br; StringTokenizer st; public MyScanner() { br = new BufferedReader(new InputStreamReader(System.in)); } String next() { while (st == null || !st.hasMoreElements()) { try { st = new StringTokenizer(br.readLine()); } catch (IOException e) { e.printStackTrace(); } } return st.nextToken(); } int nextInt() { return Integer.parseInt(next()); } long nextLong() { return Long.parseLong(next()); } double nextDouble() { return Double.parseDouble(next()); } String nextLine(){ String str = ""; try { str = br.readLine(); } catch (IOException e) { e.printStackTrace(); } return str; } int[] nextIntArray(int n){ int[]r=new int[n]; for(int i=0;i<n;++i)r[i]=nextInt(); return r; } } }