c++创建二叉树的问题

#include 
using namespace std;

class tree {
public:
    char val;
    tree* lchild;
    tree* rchild;
    void creatTree(tree* &T)
    {
        char ch;
        ch = getchar();
        if (ch == '#')
        {
            T = NULL;
        }
        else
        {
            T = new tree;
            T->val = ch;
            creatTree(T->lchild);
            creatTree(T->rchild);
        }
    }
    void VLR(tree* T)
    {
        if (T == NULL)
        {
            return;
        }
        else {
            cout << T->val;
            VLR(T->lchild);
            VLR(T->rchild);
        }
    }
       
};

int main()
{
    tree t;
    tree* T;
    t.creatTree(T);
    t.VLR(T);
}

在 void creatTree(tree* &T)中去掉&就会报错这是为什么？