bst implementation

#include<iostream>
using namespace std;
class tree{
    public:
    int data;
    tree*left;
    tree*right;
    tree(int n){
        data=n;
        left=right=NULL;
    }
};

tree*insert(tree*root,int n){
    if(!root)return new tree(n);
    if(root->data==n)return root;
    if(n < root->data)root->left=insert(root->left,n);
    else root->right=insert(root->right,n);
}

tree*deletenode(tree*root,int n){
    if(!root)return root;
    if(root->data==n){
        if(root->left==NULL)return root->right;
        else if(root->right==NULL)return root->left;
        else{
            tree*tmp=root->right;
            while(tmp->left){
                tmp=tmp->left;
            }
            tmp->left=root->left;
            root=root->right;
            return root;
        }
    }
    else if(root->data>n){
        root->left=deletenode(root->left,n);
    }
    else{
        root->right=deletenode(root->right,n);
    }
    return root;
}


void preorder(tree*root){
    if(!root)return;
    cout<<root->data<<" ";
    preorder(root->left);
    preorder(root->right);
}
void inorder(tree*root){
    if(!root)return;
    inorder(root->left);
    cout<<root->data<<" ";
    inorder(root->right);
}
void postorder(tree*root){
    if(!root)return;
    postorder(root->left);
    postorder(root->right);
    cout<<root->data<<" ";
}
int main(){
    tree*root=NULL;
    root=insert(root,2);
    root=insert(root,5);
    root=insert(root,2);
    root=insert(root,4);
    root=insert(root,9);
    root=insert(root,3);
    root=insert(root,1);
    preorder(root);
    cout<<endl;
    inorder(root);
    cout<<endl;
    postorder(root);
    cout<<endl;
    root=deletenode(root,5);
    preorder(root);
    cout<<endl;
    inorder(root);
    cout<<endl;
    postorder(root);
}