Sum of leaf nodes at minimum level

/*
  C Program 
+ Sum of leaf nodes at minimum level

*/
#include <stdio.h>

#include <stdlib.h>
 //structure of Binary Tree node
struct Node
{
	int data;
	struct Node *left, *right;
};
//Create a binary tree nodes and node fields (data,pointer) 
//And returning the reference of newly nodes
struct Node *insert(int data)
{
	//create dynamic memory to new binary tree 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; //Initially node left-pointer is NULL
		new_node->right = NULL; //Initially node right-pointer is NULL
	}
	else
	{
		printf("Memory Overflow\n");
		exit(0); //Terminate program execution
	}
	//return reference
	return new_node;
}
//Find the minimum level leaf node height
void find_height(struct Node *root, int *height, int level)
{
	if (root != NULL)
	{
		if ((root->left == NULL && root->right == NULL) && ( *height == -1 || ( *height) > level))
		{
			*height = level;
		}
		find_height(root->left, height, level + 1);
		find_height(root->right, height, level + 1);
	}
}
//Calculate sum of all leaf nodes at minimum level
int min_level_leaf_sum(struct Node *root, int level, int k)
{
	if (root != NULL && level <= k)
	{
		if (level == k && root->left == NULL && root->right == NULL)
		{
			//When get a leaf nodes are at minimum level
			return root->data;
		}
		return min_level_leaf_sum(root->left, level + 1, k) + min_level_leaf_sum(root->right, level + 1, k);
	}
	else
	{
		return 0;
	}
}
//This function are handle the request of find the sum of leaf at min depth 
void min_depth(struct Node *root)
{
	int height = -1;
	//Find the min level leaf node height
	find_height(root, & height, 0);
	int sum = min_level_leaf_sum(root, 0, height);
	printf(" Minimum level leaf nodes sum : %d \n", sum);
}
int main()
{
	struct Node *root = NULL;
	/* Make A Binary Tree
	-----------------------
	        1
	       /  \
	      2    3
	     /    /  \
	    3    1    1
	             / \
	            4   6
	           /
	          7
	*/
	//Insertion of binary tree nodes
	root = insert(1);
	root->left = insert(2);
	root->right = insert(3);
	root->right->right = insert(1);
	root->right->left = insert(1);
	root->left->left = insert(3);
	root->right->right->left = insert(4);
	root->right->right->right = insert(6);
	root->right->right->left->left = insert(7);
	min_depth(root);
	return 0;
}

Output

 Minimum level leaf nodes sum : 4