Second level pointer creates a binary tree

//==========================================Define the head
#include <iostream>
using namespace std;
struct BiTNode{
 char data;
 struct BiTNode *lchild, *rchild;//Left and right children
};
void CreateBiTree(BiTNode**T);//This must be a second level pointer and cannot be changed to bitnode * * & T
void Inorder(BiTNode* T);//Can be changed to bitnode * & T
void PreOrderTraverse(BiTNode* T);//Can be changed to bitnode * & T
void Posorder(BiTNode* T);//Can be changed to bitnode * & T
//===========================================Main function
int main(){
    cout<<"Create a tree where A->Z The character represents the data of the tree“#”Represents an empty tree:“<<endl;   
    BiTNode*T=NULL;//Define T as a first level pointer
    CreateBiTree(&T);//So, what we have to pass here is the address of T
    cout<<"First order recursive traversal:"<<endl;
    PreOrderTraverse(T);
    cout<<endl;
    cout<<"Middle order recursive traversal:"<<endl;
    Inorder(T);
    cout<<endl;
    cout<<"Subsequent recursive traversal:"<<endl;
    Posorder(T);
    cout<<endl;
    system("pause");
    return 1;
}
//=============================================First order recursion to create binary tree
void CreateBiTree(BiTNode** T){
 char ch;
 if((ch=getchar())=='#') *T=NULL;//Note: Yes * T=NULL;
 else{ 
  (*T)=new BiTNode;//Be careful
  (*T)->data=ch;//Be careful
  CreateBiTree(&(*T)->lchild);//Be careful
  CreateBiTree(&(*T)->rchild);//Be careful
 }
}
//===============================================First order recursive traversal of binary tree
void PreOrderTraverse(BiTNode* T){
 //First order recursive traversal of binary tree
 if(T){//Execute when the node is not empty
  cout<<T->data;
  PreOrderTraverse(T->lchild);//
  PreOrderTraverse(T->rchild);
 }
 else cout<<"";
}//PreOrderTraverse
//================================================Middle order ergodic binary tree
void Inorder(BiTNode* T){//Middle order recursively traversing binary tree
 if(T){//bt=null fallback
  Inorder(T->lchild);//Middle order traversal left subtree
  cout<<T->data;//Access parameters
  Inorder(T->rchild);//Middle order traversal right subtree
 }
 else cout<<"";
 }//Inorder
//=================================================Postorder recursive traversal of binary tree
void Posorder(BiTNode* T){
 if(T){
  Posorder(T->lchild);//Backward recursive traversal of left subtree
  Posorder(T->rchild);//Backward recursive traversal of right subtree
  cout<<T->data;//Access root
 }
 else cout<<"";
}
//=================================================

First level pointer creates a binary tree

//==========================================Define the head
#include <iostream>
using namespace std;
struct BiTNode{
 char data;
 struct BiTNode *lchild, *rchild;//Left and right children
};
void CreateBiTree(BiTNode* &T);
void Inorder(BiTNode* &T);
void PreOrderTraverse(BiTNode* &T);
void Posorder(BiTNode* &T);
//===========================================Main function
int main(){
    cout<<"Create a tree where A->Z The character represents the data of the tree“#”Represents an empty tree:“<<endl;   
    BiTNode*T=NULL;//
    CreateBiTree(T);//Passing the first level pointer T
    cout<<"First order recursive traversal:"<<endl;
    PreOrderTraverse(T);
    cout<<endl;
    cout<<"Middle order recursive traversal:"<<endl;
    Inorder(T);
    cout<<endl;
    cout<<"Subsequent recursive traversal:"<<endl;
    Posorder(T);
    cout<<endl;
    system("pause");
    return 1;
}
//=============================================First order recursion to create binary tree
void CreateBiTree(BiTNode* &T){
 char ch;
 if((ch=getchar())=='#')T=NULL;
 else{
  T=new BiTNode;//
  T->data=ch;//
  CreateBiTree(T->lchild);//
  CreateBiTree(T->rchild);//
 }
}
//===============================================First order recursive traversal of binary tree
void PreOrderTraverse(BiTNode* &T){
 //First order recursive traversal of binary tree
 if(T){//Execute when the node is not empty
  cout<<T->data;
  PreOrderTraverse(T->lchild);//
  PreOrderTraverse(T->rchild);
 }
 else cout<<"";
}//PreOrderTraverse
//================================================Middle order ergodic binary tree
void Inorder(BiTNode* &T){//Middle order recursively traversing binary tree
 if(T){//bt=null fallback
  Inorder(T->lchild);//Middle order traversal left subtree
  cout<<T->data;//Access parameters
  Inorder(T->rchild);//Middle order traversal right subtree
 }
 else cout<<"";
 }//Inorder
//=================================================Postorder recursive traversal of binary tree
void Posorder(BiTNode* &T){
 if(T){
  Posorder(T->lchild);//Backward recursive traversal of left subtree
  Posorder(T->rchild);//Backward recursive traversal of right subtree
  cout<<T->data;//Access root node
 }
 else cout<<"";
}
//=================================================

Summary: the difference between the two lies only in the difference of creating this function in binary tree (respectively, void CreateBiTree(BiTNode**T), void createbitree (bitnode * & T)), and the difference when the main function calls this function (respectively, createbitree (& T), CreateBiTree(T)); for traversal, they are the same.
First level pointer must use reference;
Second level pointer cannot be referenced;
For secondary pointers:
Establish:

void CreateBiTree(BiTNode** T){
 char ch;
 if((ch=getchar())=='#') *T=NULL;//Note: Yes * T=NULL;
 else{ 
  (*T)=new BiTNode;//Be careful
  (*T)->data=ch;//Be careful
  CreateBiTree(&(*T)->lchild);//Be careful
  CreateBiTree(&(*T)->rchild);//Be careful
 }
}

Call:

BiTNode*T=NULL;
CreateBiTree(&T)

For first level pointers:
Establish:

void CreateBiTree(BiTNode* &T){
 char ch;
 if((ch=getchar())=='#')T=NULL;
 else{
  T=new BiTNode;//
  T->data=ch;//
  CreateBiTree(T->lchild);//
  CreateBiTree(T->rchild);//
 }
}

Call:

BiTNode*T=NULL;
CreateBiTree(T)