Insertion in binary search tree using recursion in c

C program for Insertion in binary search tree using recursion. Here problem description and explanation.

// Include header file
#include <stdio.h>
#include <stdlib.h>

// C program for
// Insertion in binary search tree by using recursion
typedef struct TreeNode
{
	// Define useful field of TreeNode
	int data;
	struct TreeNode * left;
	struct TreeNode * right;
}TreeNode;

TreeNode * getTreeNode(int data)
{
	// Create dynamic memory of TreeNode
	TreeNode * ref = (TreeNode * ) malloc(sizeof(TreeNode));
	if (ref == NULL)
	{
		// Failed to create memory 
		return NULL;
	}
	ref->data = data;
	ref->left = NULL;
	ref->right = NULL;
	return ref;
}
typedef struct BinarySearchTree
{
	// Define useful field of BinarySearchTree
	struct TreeNode * root;
}BinarySearchTree;

BinarySearchTree * getBinarySearchTree()
{
	// Create dynamic memory of BinarySearchTree
	BinarySearchTree * ref = 
      (BinarySearchTree * ) malloc(sizeof(BinarySearchTree));
	if (ref == NULL)
	{
		// Failed to create memory 
		return NULL;
	}
	ref->root = NULL;
	return ref;
}
// Insert a node element
TreeNode * addNode(TreeNode * node, int data)
{
	if (node != NULL)
	{
		if (node->data >= data)
		{
			// When new element is smaller or
			// equal to current node
			node->left = addNode(node->left, data);
		}
		else
		{
			// When new element is higher to current node
			node->right = addNode(node->right, data);
		}
		// important to manage root node
		return node;
	}
	else
	{
		return getTreeNode(data);
	}
}
// Display preorder
void preorder(TreeNode * node)
{
	if (node != NULL)
	{
		// Display node value
		printf(" %d ", node->data);
		// Visit to left subtree
		preorder(node->left);
		// Visit to right subtree
		preorder(node->right);
	}
}
void inorder(TreeNode * node)
{
	if (node != NULL)
	{
		// Visit to left subtree
		inorder(node->left);
		// Display node value
		printf(" %d ", node->data);
		// Visit to right subtree
		inorder(node->right);
	}
}
void postorder(TreeNode * node)
{
	if (node != NULL)
	{
		// Visit to left subtree
		postorder(node->left);
		// Visit to right subtree
		postorder(node->right);
		// Display node value
		printf(" %d ", node->data);
	}
}
int main()
{
	BinarySearchTree * tree = getBinarySearchTree();
	/*
	         10
	        / \
	       /   \
	      4     15
	     / \   /
	    3   5 12
	    -------------
	    Build binary search tree
	*/
	tree->root = addNode(tree->root, 10);
	addNode(tree->root, 4);
	addNode(tree->root, 3);
	addNode(tree->root, 5);
	addNode(tree->root, 15);
	addNode(tree->root, 12);
	// Display tree nodes
	printf("Preorder \n");
	preorder(tree->root);
	printf("\nInorder \n");
	inorder(tree->root);
	printf("\nPostorder \n");
	postorder(tree->root);
}

Output

Preorder
 10  4  3  5  15  12
Inorder
 3  4  5  10  12  15
Postorder
 3  5  4  12  15  10