C++ tree data structure Access violation with String - c++

Question

I am trying to make a tree data structure with c++. Originally I tested with int data, it was going fine. However, when I try to use a string data type, it keeps showing an unhandled exception. It said read access violation, this was 0x5D. I don't know what is causing the error. The complete same code only changing int to string causes the violation.
Main:
#include <bits/stdc++.h>
#include "Tree.h"
using namespace std;
int main()
{
Tree A;
int choice; bool isCre=0;
cout << "Input choice : ";
while (cin >> choice) {
switch (choice)
{
case 1:
if (!isCre) {
A.create_tree(); isCre = 1;
break;
}
else {
A.add_tree();
break;
}
case 2:
A.delete_tree(); break;
case 3:
A.modify_tree(); break;
case 4:
A.display_tree(); break;
}
cout << "Input choice : ";
}
}
Header file:
#ifndef TREE_H
#define TREE_H
#include <bits/stdc++.h>
using namespace std;
class Tree
{
private:
struct Tre
{
Tre* parent; Tre* right; Tre* left;
string data;
Tre(Tre* parent, string data)
{
this->parent = parent;
this->data = data;
left = right = NULL;
}
};
Tre* root;
Tre* create(Tre*& root, string data)
{
Tre* p;
p = new Tre(NULL, data);
root = p;
return root;
}
void dis(Tre* node)
{
if (node == NULL)
return;
cout << node->data << endl;
dis(node->left);
dis(node->right);
}
Tre* search(Tre* node, string data)
{
if (node == NULL)
return NULL;
if (node != NULL && node->data == data)
return node;
/* then recur on left subtree */
Tre* p = search(node->left, data);
// node found, no need to look further
if (p != NULL && p->data == data) return p;
/* node is not found in left,
so recur on right subtree */
Tre* q = search(node->right, data);
if (q != NULL && q->data == data) return q;
}
Tre* add(Tre* root, string find, string input)
{
Tre* p = root;
p = search(root, find);
if (p->left != NULL)
{
p->right = new Tre(p, input);
//p->left = new Tre(p, input);
}
else if (p->left == NULL)
{
p->left = new Tre(p, input);
//p->right = new Tre(p, input);
}
return root;
}
Tre* del(Tre* root, string data)
{
Tre* p = root, * q;
p = search(root, data);
q = p->parent;
if (q->right != NULL && q->right->data == data)
{
q->right = NULL;
delete p;
}
else if (q->left->data == data)
{
q->left = NULL;
delete p;
}
return root;
}
Tre* modify(Tre* root, string find, string input)
{
Tre* p = root;
p = search(p, find);
p->data = input;
return root;
}
public:
void create_tree();
void display_tree();
void add_tree();
void delete_tree();
void modify_tree();
};
#endif
#endif
Implementation file:
#include "Tree.h"
void Tree::create_tree()
{
string data;
cout << "Input data : "; cin >> data;
create(root, data);
}
void Tree::display_tree()
{
dis(root);
}
void Tree::add_tree()
{
string find, input;
cout << "Parent data : "; cin >> find;
cout << "New data : "; cin >> input;
add(root, find, input);
}
void Tree::delete_tree()
{
string data;
cout << "Delete data : "; cin >> data;
del(root, data);
}
void Tree::modify_tree()
{
string find, input;
cout << "Find data : "; cin >> find;
cout << "New data : "; cin >> input;
modify(root, find, input);
}