import java.io.*;
import java.util.ArrayDeque;
import java.util.Arrays;
import java.util.StringJoiner;
import java.util.StringTokenizer;
import java.util.function.Function;

public class Main {

    static int N, K;
    static int[] A, B;

    public static void main(String[] args) {
        FastScanner sc = new FastScanner(System.in);
        N = sc.nextInt();
        K = sc.nextInt();
        A = new int[N-1];
        B = new int[N-1];
        for (int i = 0; i < N - 1; i++) {
            A[i] = sc.nextInt()-1;
            B[i] = sc.nextInt()-1;
        }

        System.out.println(solve());
    }

    static int[][] adjB(int n, int[] from, int[] to) {
        int[][] adj = new int[n][];
        int[] cnt = new int[n];
        for (int f : from) {
            cnt[f]++;
        }
        for (int t : to) {
            cnt[t]++;
        }
        for (int i = 0; i < n; i++) {
            adj[i] = new int[cnt[i]];
        }
        for (int i = 0; i < from.length; i++) {
            adj[from[i]][--cnt[from[i]]] = to[i];
            adj[to[i]][--cnt[to[i]]] = from[i];
        }
        return adj;
    }

    static class Node {
        int parent, a;

        public Node(int parent, int a) {
            this.parent = parent;
            this.a = a;
        }
    }

    static Node[] orderFromRoot(int N, int[][] G, int root) {
        ArrayDeque<Node> q = new ArrayDeque<>();
        Node[] ret = new Node[N];
        int idx = 0;
        q.add(new Node(-1, root));
        while(!q.isEmpty()) {
            Node n = q.poll();
            ret[idx++] = n;
            for (int next : G[n.a]) {
                if( next == n.parent ) continue;

                q.add(new Node(n.a, next));
            }
        }
        return ret;
    }

    static int solve() {
        int[][] G = adjB(N, A, B);

        FermatCombination fc = new FermatCombination(K+1);
        int ans = 1;
        for (Node node : orderFromRoot(N, G, 0)) {
            int req;
            int suc;
            int sib;
            if( node.parent == -1 ) { // parent
                suc = 1;
                sib = G[node.a].length;
                req = 1 + sib;
            } else {
                suc = 2;
                sib = G[node.a].length-1;
                req = suc + sib;
            }

            if( K < req ) return 0;
            int comb = mul(fc.factorial[K-suc], fc.inverse[K-suc-sib]);
            ans = mul(ans, comb);
        }

        return mul(ans, K);
    }

    static int MOD = 1_000_000_007;

    static int pow(int base, long exp) {
        if (exp == 0) return 1;

        int ans = 1;
        base %= MOD;
        while (exp > 0) {
            if ((exp & 1) == 1) {
                ans = mul(ans, base);
            }

            base = mul(base, base);
            exp = exp >> 1;
        }
        return ans;
    }

    static int sub(int a, int b) {
        int c = a - b;
        if (c < 0) c += MOD;
        return c;
    }

    static int div(int a, int b) {
        return mul(a, pow(b, MOD - 2));
    }

    static int add(int a, int b) {
        int c = a + b;
        if (c >= MOD) c %= MOD;
        return c;
    }

    static int mul(int a, int b) {
        long c = (long) a * b;
        if (c >= MOD) c %= MOD;
        return (int) c;
    }

    static class FermatCombination {
        private final int size;
        private final int[] factorial; // n -> factorial(n)
        private final int[] inverse;   // n -> inverse(factorial(n))

        FermatCombination(int size) {
            this.size = size;
            factorial = new int[size + 1];
            inverse = new int[size + 1];

            init();
        }

        private void init() {
            factorial[0] = 1;
            factorial[1] = 1;
            inverse[0] = 1;
            inverse[1] = 1;
            for (int i = 2; i <= size; i++) {
                factorial[i] = mul(factorial[i - 1], i);
                inverse[i] = pow(factorial[i], MOD - 2);
            }
        }

        int comb(int n, int k) {
            if (n > size) throw new RuntimeException("wtf : size=" + size + " n=" + n);
            return mul(mul(factorial[n], inverse[k]), inverse[n - k]);
        }

        // 重複組み合わせ
        // k種類からn個選ぶ場合の数
        int hcomb(int k, int n) {
            return comb(k + n - 1, n);
        }

        int group(int n, int g, int k) {
            // C(n, g) * C(n-g, g)... / k!
            // n! / (n-gk)! / g! ^ k / k!
            int ret = factorial[n];             // n!
            ret = mul(ret, inverse[n - g * k]);   // 1 / (n-gk)!
            ret = mul(ret, pow(inverse[g], k)); // 1 / (g! ^ k)
            ret = mul(ret, inverse[k]);         // 1 / k!
            return ret;
        }
    }

    @SuppressWarnings("unused")
    static class FastScanner {
        private BufferedReader reader;
        private StringTokenizer tokenizer;

        FastScanner(InputStream in) {
            reader = new BufferedReader(new InputStreamReader(in));
            tokenizer = null;
        }

        String next() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        String nextLine() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    return reader.readLine();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken("\n");
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        int nextInt() {
            return Integer.parseInt(next());
        }

        int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        int[] nextIntArray(int n, int delta) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt() + delta;
            return a;
        }

        long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        }
    }

    static <A> void writeLines(A[] as, Function<A, String> f) {
        PrintWriter pw = new PrintWriter(System.out);
        for (A a : as) {
            pw.println(f.apply(a));
        }
        pw.flush();
    }

    static void writeLines(int[] as) {
        PrintWriter pw = new PrintWriter(System.out);
        for (int a : as) pw.println(a);
        pw.flush();
    }

    static void writeLines(long[] as) {
        PrintWriter pw = new PrintWriter(System.out);
        for (long a : as) pw.println(a);
        pw.flush();
    }

    static int max(int... as) {
        int max = Integer.MIN_VALUE;
        for (int a : as) max = Math.max(a, max);
        return max;
    }

    static int min(int... as) {
        int min = Integer.MAX_VALUE;
        for (int a : as) min = Math.min(a, min);
        return min;
    }

    static void debug(Object... args) {
        StringJoiner j = new StringJoiner(" ");
        for (Object arg : args) {
            if (arg instanceof int[]) j.add(Arrays.toString((int[]) arg));
            else if (arg instanceof long[]) j.add(Arrays.toString((long[]) arg));
            else if (arg instanceof double[]) j.add(Arrays.toString((double[]) arg));
            else if (arg instanceof Object[]) j.add(Arrays.toString((Object[]) arg));
            else j.add(arg.toString());
        }
        System.err.println(j.toString());
    }
}


Measured memory_bytes: 52456