C++我创建了一个类描述二叉树，但是析构时内存报错，能帮我看看怎么回事吗？

#ifndef BTREE_H_
#define BTREE_H_

#include

using namespace std;

struct bintree
{
  char ch;
  bintree * ltree;
  bintree * rtree;
};
  

class bt
{
  private:
  bintree *root;
  public:
  bt(char c = 'A');
  bintree *rroot();
  void insert(bintree * b);
  void presearch(bintree * b);
  void insearch(bintree * b);
  void nexsearch(bintree * b);
  void return_ad(bintree *b);
  ~bt();
  
};











#endif


#include"btree.h"


bt::bt(char c)
{
  root = new bintree;
  root->ch = c;
  
}


bintree * bt::rroot(){return root;}


void bt::insert(bintree * b) 
{
cout<< "The node "<< b->ch<<" has a left node ? "<>choice;
if(choice == 'Y')
{
  bintree * i = new bintree;
  cout<<"Please enter the content of left node : "<< endl;
  cin>>choice;
  b->ltree = i;
  i->ch =choice;
  insert(i);
}
else
  b->ltree = NULL;

cout<< "The node "<< b->ch<<" has a right node ?"<>choice;
if(choice == 'Y')
{
  bintree * j= new bintree;
  cout<<"Please enter the content of right node : "<< endl;
  cin>>choice;
  b->rtree = j;
  j->ch =choice;
  insert(j);
}
else
  b->rtree = NULL;
}


void bt::presearch(bintree * tree)
{
  if(tree)
{
  cout<<" "<ch<<" ";
  presearch(tree->ltree);
  presearch(tree->rtree);
}
} 

void bt::insearch(bintree * tree)
{
  if(tree)
{
    insearch(tree->ltree);
    cout<<" "<ch<<" ";
    insearch(tree->rtree);
}
}

void bt::nexsearch(bintree * tree)
{
  if(tree)
{
    nexsearch(tree->ltree);
    nexsearch(tree->rtree);
    cout<<" "<ch<<" ";
 
}
}

void bt::delete_tree(bintree * tree)
{
  if(tree)
  {
  delete_tree(tree->ltree);
  delete_tree(tree->ltree);
  delete tree;
  }
 }


bt::~bt()
{
delete_tree(root);
}