想要给insert函数里的int &x设置默认值root

struct Tread
{
	int root;
	inline void insert(int &x,int y)
	{
		if(!x){x=New(y);return;}
		if(y==v[x])
			c[x]++;
		else
		{
			int d=y>v[x];
			insert(ch[x][d],y);
			if(r[x]<r[ch[x][d]])
				ro(x,d^1);
		}
		up(x);
	}
}T;