Insertion in binary search tree without recursion in kotlin

Kotlin program for Insertion in binary search tree without recursion. Here problem description and other solutions.

// Kotlin program for
// iterative insert in binary search tree
class TreeNode
{
	var data: Int;
	var left: TreeNode ? ;
	var right: TreeNode ? ;
	constructor(data: Int)
	{
		this.data = data;
		this.left = null;
		this.right = null;
	}
}
class BinarySearchTree
{
	var root: TreeNode ? ;
	constructor()
	{
		this.root = null;
	}
	//insert a element
	fun addNode(data: Int): Unit
	{
		// Create a new node
		val node: TreeNode = TreeNode(data);
		if (this.root == null)
		{
			// When adds a first node in bst
			this.root = node;
		}
		else
		{
			var find: TreeNode ? = this.root;
			// Add new node to proper position
			while (find != null)
			{
				if (find.data >= data)
				{
					if (find.left == null)
					{
						// When left child empty
						// So add new node here
						find.left = node;
						return;
					}
					else
					{
						// Otherwise
						// Visit left sub-tree
						find = find.left;
					}
				}
				else
				{
					if (find.right == null)
					{
						// When right child empty
						// So add new node here
						find.right = node;
						return;
					}
					else
					{
						// Visit right sub-tree
						find = find.right;
					}
				}
			}
		}
	}
	// Display preorder
	fun preorder(node: TreeNode ? ): Unit
	{
		if (node != null)
		{
			// Display node value
			print("  " + node.data);
			// Visit to left subtree
			this.preorder(node.left);
			// Visit to right subtree
			this.preorder(node.right);
		}
	}
	fun inorder(node: TreeNode ? ): Unit
	{
		if (node != null)
		{
			// Visit to left subtree
			this.inorder(node.left);
			// Display node value
			print("  " + node.data);
			// Visit to right subtree
			this.inorder(node.right);
		}
	}
	fun postorder(node: TreeNode ? ): Unit
	{
		if (node != null)
		{
			// Visit to left subtree
			this.postorder(node.left);
			// Visit to right subtree
			this.postorder(node.right);
			// Display node value
			print("  " + node.data);
		}
	}
}
fun main(args: Array < String > ): Unit
{
	val tree: BinarySearchTree = BinarySearchTree();
	/*
	         10
	        / \
	       /   \
	      4     15
	     / \   /
	    3   5 12
	    -------------
	    Build binary search tree

	*/
	tree.addNode(10);
	tree.addNode(4);
	tree.addNode(3);
	tree.addNode(5);
	tree.addNode(15);
	tree.addNode(12);
	// Display tree nodes
	println("Preorder ");
	tree.preorder(tree.root);
	println("\nInorder ");
	tree.inorder(tree.root);
	println("\nPostorder ");
	tree.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