#include <bits/stdc++.h>
using namespace std;
template <class htpe, class cmp>
using heap = priority_queue<htpe, vector<htpe>, cmp>;
template <class htpe>
using min_heap = heap<htpe, greater<htpe> >;
template <class htpe>
using max_heap = heap<htpe, less<htpe> >;
const int INF = 1791791791;
const long long INFLL = 1791791791791791791ll;
template <int input_buf_size, int output_buf_size>
class FastIO {
  char cbuf[input_buf_size + 1];
  int icur = 0;
  inline bool go_to_next_token() {
    while (cbuf[icur] == ' ' || cbuf[icur] == '\n') icur++;
    while (cbuf[icur] == 0) {
      icur = 0;
      if (fgets(cbuf, sizeof(cbuf), stdin) != cbuf) return false;
      while (cbuf[icur] == ' ' || cbuf[icur] == '\n') icur++;
    }
    return true;
  }

 public:
  string readString() {
    assert(go_to_next_token());
    string ans;
    while (cbuf[icur] != ' ' && cbuf[icur] != '\n' && cbuf[icur] != 0)
      ans.push_back(cbuf[icur++]);
    ans.shrink_to_fit();
    return ans;
  }
  template <class int_type>
  int_type readInt() {
    assert(go_to_next_token());
    int_type x = 0;
    bool m = cbuf[icur] == '-';
    if (m) icur++;
    while ('0' <= cbuf[icur] && cbuf[icur] <= '9') {
      x *= 10;
      x += (cbuf[icur] - '0');
      icur++;
    }
    if (m) x = -x;
    return x;
  }
  bool seekEof() { return !go_to_next_token(); }

 private:
  char obuf[output_buf_size + 1];
  int ocur = 0;
  inline void write_string(const char *str, size_t sz = 0) {
    if (sz == 0) sz = strlen(str);
    if (ocur + sz > output_buf_size) {
      fputs(obuf, stdout);
      fputs(str, stdout);
      ocur = 0;
      obuf[0] = 0;
      return;
    }
    strcpy(obuf + ocur, str);
    ocur += sz;
    obuf[ocur] = 0;
  }

 public:
  template <class int_type>
  void writeInt(int_type x, bool sp = true) {
    char buf[21];
    int c = 0;
    if (x < 0) {
      buf[c++] = '-';
      x = -x;
    }
    int s = c;
    if (x == 0) {
      buf[c++] = '0';
    }
    while (x > 0) {
      buf[c++] = (x % 10) + '0';
      x /= 10;
    }
    for (int i = 0; 2 * i < c - s; i++) {
      swap(buf[s + i], buf[c - 1 - i]);
    }
    buf[c] = 0;
    write_string(buf, c);
    if (sp) write_string(" ", 1);
  }
  void writeString(string s, bool space = true) {
    write_string(s.c_str(), s.size());
    if (space) write_string(" ", 1);
  }
  void writeEndl() { write_string("\n", 1); }
  void flush() {
    fputs(obuf, stdout);
    ocur = 0;
    obuf[0] = 0;
  }

 private:
  bool lflush;

 public:
  FastIO(bool local_flush) {
    obuf[0] = 0;
    lflush = local_flush;
  }
  ~FastIO() { fputs(obuf, stdout); }
};
FastIO<10000000, 10000000> IO(true);
const int maxn = 1e5 + 179;
const int maxi = 11;
const long long MOD = 1e9 + 7;
long long m, k;
vector<int> graph[maxn];
long long dp[maxn][maxi][3];
void dfs(int v, int par) {
  for (int u : graph[v]) {
    if (u != par) dfs(u, v);
  }
  dp[v][0][0] = k - 1;
  dp[v][1][1] = 1;
  dp[v][0][2] = m - k;
  for (int u : graph[v]) {
    if (u != par) {
      long long ndp[maxi][3];
      for (int i = 0; i < ((int)(maxi)); ++i) {
        for (int j = 0; j < ((int)(3)); ++j) ndp[i][j] = 0;
      }
      for (int i = 0; i < ((int)(maxi)); ++i) {
        for (int j = 0; j < ((int)(i + 1)); ++j) {
          ndp[i][0] +=
              dp[v][i - j][0] * (dp[u][j][0] + dp[u][j][1] + dp[u][j][2]);
          ndp[i][0] %= MOD;
          ndp[i][1] += dp[v][i - j][1] * dp[u][j][0];
          ndp[i][1] %= MOD;
          ndp[i][2] += dp[v][i - j][2] * (dp[u][j][0] + dp[u][j][2]);
          ndp[i][2] %= MOD;
        }
      }
      for (int i = 0; i < ((int)(maxi)); ++i) {
        for (int j = 0; j < ((int)(3)); ++j) dp[v][i][j] = ndp[i][j];
      }
    }
  }
}
int main() {
  int n = IO.readInt<int>();
  m = IO.readInt<int>();
  for (int i = 0; i < ((int)(n - 1)); ++i) {
    int u = IO.readInt<int>() - 1;
    int v = IO.readInt<int>() - 1;
    graph[u].push_back(v);
    graph[v].push_back(u);
  }
  k = IO.readInt<int>();
  int x = IO.readInt<int>();
  dfs(0, -1);
  long long ans = 0;
  for (int i = 0; i < ((int)(x + 1)); ++i) {
    for (int j = 0; j < ((int)(3)); ++j) ans += dp[0][i][j];
    ans %= MOD;
  }
  IO.writeInt(ans);
  IO.writeEndl();
  return 0;
}
