need help finding error in binary tree code

gbd says the segmentation fault is being generated in the insert
function.

//CONSTRUCTOR
        tree():data(value_type()), left(0), right(0){};
        tree(value_type vt, tree* l = 0, tree* r = 0):
            data(vt), left(l), right(r) {};

//PRIVATE MEMBERS

        value_type data;

        tree *left;

        tree *right;

//INSERT AND ADD NODE FUNCTIONS

tree::tree* tree::newNode(value_type new_data){
        tree* node = new tree (data);
        node->data = data;
        node->left = 0;
        node->right= 0;
        return node;
    }

    tree::tree* tree::insert(tree* node, value_type new_data){
        if (node == 0){
            return(newNode(data));
        }else

            if(data <= node->data){
                node->left = insert(node->left, data);
        }else
        node->right = insert(node->right, data);
        return node;
    }

//DRIVER

#include<iostream>
#include "tree.h"
using namespace std;
using namespace abrowning_13;

int main(){

    tree t1;
    tree* tree_ptr;
    int user_input;

        while(cin.peek() != EOF){
            t1.insert(tree_ptr, user_input);
        }
            t1.inorder_print(tree_ptr);

return 0;

}