#include <bits/stdc++.h>
using namespace std;
long long BE(long long a, long long b) {
  long long ans = 1, i;
  for (i = a; b; b >> 1, i = i * i) {
    if (b & 1) ans += ans * i;
  }
  return ans;
}
const long long MOD = (long long)1e9 + 7;
const int N = (long long)1e5 + 2;
const int M = (long long)4e5;
long long dp[N][15][4];
long long m, x, k;
std::vector<long long> graph[N];
void dfs(long long u, long long p) {
  long long bit[2][15][4] = {0};
  long long parity = 0;
  bit[parity][0][0] = k - 1, bit[parity][0][2] = m - k;
  bit[parity][1][1] = 1;
  for (auto v : graph[u]) {
    if (p - v) {
      dfs(v, u);
      parity = 1 - parity;
      for (long long i = 0; i <= x; i++)
        for (long long j = 0; j < 3; j++) bit[parity][i][j] = 0;
      for (long long i = 0; i <= x; i++) {
        for (long long j = 0; j <= i; j++) {
          bit[parity][i][0] =
              (bit[parity][i][0] +
               (dp[v][i - j][0] + dp[v][i - j][1] + dp[v][i - j][2]) *
                   bit[1 - parity][j][0]) %
              MOD;
          bit[parity][i][1] =
              (bit[parity][i][1] + (dp[v][i - j][0]) * bit[1 - parity][j][1]) %
              MOD;
          bit[parity][i][2] =
              (bit[parity][i][2] +
               (dp[v][i - j][0] + dp[v][i - j][2]) * bit[1 - parity][j][2]) %
              MOD;
        }
      }
    }
  }
  for (long long i = 0; i <= x; i++)
    for (long long j = 0; j < 3; j++) dp[u][i][j] = bit[parity][i][j];
  return;
}
int main() {
  long long n;
  cin >> n >> m;
  for (long long i = 1; i < n; i++) {
    long long u, v;
    cin >> u >> v;
    graph[v].push_back(u);
    graph[u].push_back(v);
  }
  cin >> k >> x;
  dfs(1, -1);
  long long ans = 0;
  for (long long i = 0; i <= x; i++)
    for (long long j = 0; j < 3; j++) ans = (ans + dp[1][i][j]) % MOD;
  printf("%lld\n", ans);
  return 0;
}
