Find top three elements in binary tree

/*
  C Program  
  Find top three elements in binary tree
*/
#include <stdio.h>

#include <stdlib.h>

//Binary Tree node
struct Node
{
	int data;
	struct Node *left, *right;
};
//This is creating a binary tree node and return this
struct Node *add_node(int data)
{
	// Create dynamic node
	struct Node *new_node = (struct Node *) malloc(sizeof(struct Node));
	if (new_node != NULL)
	{
		//Set data and pointer values
		new_node->data = data;
		new_node->left = NULL;
		new_node->right = NULL;
	}
	else
	{
		//This is indicates, segmentation fault or memory overflow problem
		printf("Memory Overflow\n");
	}
	//return new node
	return new_node;
}
//Recursive function
//Display preorder view of binary tree
void pre_order(struct Node *node)
{
	if (node != NULL)
	{
		//Print node value
		printf("  %d", node->data);
		pre_order(node->left);
		pre_order(node->right);
	}
}
//Find top three largest nodes in binary tree
void top_three(struct Node *node, 
               struct Node **first, 
               struct Node **second, 
               struct Node **third)
{
	if (node != NULL)
	{
		if ( *first == NULL)
		{
			// First node of tree
			*first = node;
		}
		else if (( *first)->data < node->data)
		{
			//When get new first largest node
			//Interchange the node values
			*third = *second;*second = *first;*first = node;
		}
		else if ( *second == NULL)
		{
			if (( *first)->data != node->data)
			{
				//Get second largest node
				*second = node;
			}
		}
		else
		{
			if (( *second)->data < node->data && ( *first)->data > node->data)
			{
				//When we get new second largest
				//Replace the third node with the second node
				*third = *second;
				//This is new second largest element
				*second = node;
			}
			else if ( *third == NULL)
			{
				if (( *second)->data > node->data && ( *first)->data > node->data)
				{
					//Get the third largest node
					*third = node;
				}
			}
			else if (( *third)->data < node->data 
                     && ( *first)->data > node->data 
                     && ( *second)->data > node->data)
			{
				*third = node;
			}
		}
		// Recursively, execute left and right subtree
		top_three(node->left, first, second, third);
		top_three(node->right, first, second, third);
	}
}
// This are handle the request to finding top three nodes in binary tree
void find_node(struct Node *root)
{
	if (root == NULL)
	{
		return;
	}
	//Display tree elements
	printf("\n Preorder : ");
	pre_order(root);
	//Set the initial all three nodes
	struct Node *first = NULL;
	struct Node *second = NULL;
	struct Node *third = NULL;
	// Find three largest element
	top_three(root, &first, &second, &third);
	// Display calculated result
	printf("\n First  : %d ", first->data);
	if (second != NULL && second != first && second->data < first->data)
	{
		printf("\n Second : %d ", second->data);
	}
	else
	{
		printf("\n Second : None ");
	}
	if (third != NULL 
        && third != second 
        && third != first 
        && third->data < second->data)
	{
		printf("\n Third  : %d \n", third->data);
	}
	else
	{
		printf("\n Third  : None \n");
	}
}
int main()
{
	struct Node *root1 = NULL;
	struct Node *root2 = NULL;
	/*
	Construct Binary Tree
	-----------------------
	      10
	     /   \
	    6     8
	   / \   / \
	  2   3 7   5
	 /       \   \
	9        -6   13
	*/
	//Add nodes
	root1 = add_node(10);
	root1->left = add_node(6);
	root1->left->left = add_node(2);
	root1->right = add_node(8);
	root1->right->right = add_node(5);
	root1->right->left = add_node(7);
	root1->right->left->right = add_node(-6);
	root1->left->right = add_node(3);
	root1->left->left->left = add_node(9);
	root1->right->right->right = add_node(13);
	find_node(root1);
	/*  
	Construct Tree
	--------------
	     1
	   /  \
	  1    2
	 /    /  \
	1    2    2
	*/
	//Add second tree node
	root2 = add_node(1);
	root2->left = add_node(1);
	root2->right = add_node(2);
	root2->right->right = add_node(2);
	root2->right->left = add_node(2);
	root2->left->left = add_node(1);
	find_node(root2);
	return 0;
}

Output

 Preorder :   10  6  2  9  3  8  7  -6  5  13
 First  : 13
 Second : 10
 Third  : 9

 Preorder :   1  1  1  2  2  2
 First  : 2
 Second : 1
 Third  : None