#include <bits/stdc++.h>
using namespace std;
const long long infl = 1e18 + 5;
long long int n, m, k, q, x, y, f, val, t = 1, i, j;
long long int ind = -1, cnt, sz, sm, ans, mx = -1, mn = infl;
long long int a[100004], temp[3][11], dp[100004][3][11];
int vis[100004];
vector<long long int> g[100004];
void dfs(int u) {
  vis[u] = 1;
  int i, j;
  dp[u][0][0] = k - 1;
  dp[u][1][1] = 1;
  dp[u][2][0] = m - k;
  for (auto it : g[u]) {
    if (vis[it]) continue;
    dfs(it);
    for (i = 0; i < 3; i++) {
      for (j = 0; j < x + 1; j++) {
        temp[i][j] = 0;
      }
    }
    for (i = 0; i < x + 1; i++) {
      for (j = 0; i + j <= x; j++) {
        temp[0][i + j] +=
            (dp[u][0][i] * (dp[it][0][j] + dp[it][1][j] + dp[it][2][j])) %
            1000000007;
        temp[1][i + j] += (dp[u][1][i] * (dp[it][0][j])) % 1000000007;
        temp[2][i + j] +=
            (dp[u][2][i] * (dp[it][0][j] + dp[it][2][j])) % 1000000007;
        temp[0][i + j] %= 1000000007;
        temp[1][i + j] %= 1000000007;
        temp[2][i + j] %= 1000000007;
      }
    }
    for (i = 0; i < 3; i++) {
      for (j = 0; j < x + 1; j++) {
        dp[u][i][j] = temp[i][j];
      }
    }
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  if (fopen("inp.txt", "r")) {
    freopen("myfile.txt", "w", stdout);
    freopen("inp.txt", "r", stdin);
  }
  cin >> n >> m;
  for (i = 0; i < n - 1; i++) {
    cin >> x >> y;
    x--;
    y--;
    g[x].push_back(y);
    g[y].push_back(x);
  }
  cin >> k >> x;
  dfs(0);
  for (i = 0; i < 3; i++) {
    for (j = 0; j < x + 1; j++) {
      ans += dp[0][i][j];
      ans %= 1000000007;
    }
  }
  cout << ans;
  return 0;
}
