问题

void getsum() { //下传节点的sum
	for (int i = 1; i <= m; i++) {
		int x = ord[i]; ll now = 1;
		for (int j = head[x]; j; j = pre[j]) {
			int y = to[j];
			b[y].sum = (b[y].sum + b[x].sum * now % mod) % mod;
			now = now * b[y].mul % mod;//这里
		}
	}
}