Program for doing traversals on the expression tree

#include<iostream>
#include<iomanip>
#include<cstdlib>
#include<queue>
using namespace std;
class Node
{
 public:
  char data;
  Node *Left;
  Node *Right;
};
class Tree : public Node
{
 public:
  Node *root=new Node;
  string s;
  int a=0;
  int *pos=&a;
  
  
  Tree()  // constructor
  {
   cout<<"enter string : ";
   getline(cin,s);
  }
  

  void tr()   
  {
   MakeTree(s,pos,root);
   
  }

  void MakeTree(string expr, int *pos, Node *node)
  {
      if(expr[*pos] == '(')
      {
          (*pos)++;
          node->Left = new Node;
          node->Left->Left = NULL;
          node->Left->Right = NULL;
          MakeTree(expr,pos,node->Left);
          MakeTree(expr, pos, node);
          return;
      }

      if((expr[*pos] >= '0' && expr[*pos] <= '9') || (expr[*pos] >= 'a' && expr[*pos] <= 'z') || (expr[*pos] >= 'A' && expr[*pos] <= 'Z'))
      {
          node->data = expr[*pos];
          (*pos)++;
          return;
      }

      if(expr[*pos] == '+' || expr[*pos] == '-' || expr[*pos] == '*' || expr[*pos] == '/')
      {
          node->data = expr[*pos];
          (*pos)++;
    node->Right = new Node;
          node->Right->Left = NULL;
          node->Right->Right = NULL;
          MakeTree(expr, pos, node->Right);
      }

      if(expr[*pos] == ')')
          {
               (*pos)++;
              return;
          }
  }

  
   
  void pretrvsal()
   {
    prefix(root);
   }

  void prefix(Node *root)
   {
    if(root==NULL)
    {
     return ;
    }
    cout<<" "<<root->data<<" ";
    prefix(root->Left);
    prefix(root->Right);

   }

  void posttrvsal()
   {
    postfix(root);
   }

  void postfix(Node *root)
   {
    if(root==NULL)
    {
     return ;
    }

    postfix(root->Left);
    postfix(root->Right);
    cout<<" "<<root->data<<" ";
    return ;
   }

  void intrvsal()
   {
    infix(root);
   }

  void infix(Node *root)
   {
    if(root==NULL)
    {
     return ;
    }

    infix(root->Left);
    cout<<" "<<root->data<<" ";
    infix(root->Right);
    return ;

   }
  
  
};
int main()
{
 Tree t;
 t.tr();
 cout<<"prefix : ";t.pretrvsal();cout<<endl;
 cout<<"postfix : ";t.posttrvsal(); cout<<endl;              
    cout<<"infix : ";t.intrvsal();cout<<endl;

return 0;
}