Insertion in binary search tree using recursion in typescript

Ts program for Insertion in binary search tree using recursion. Here more information.

// TypeScript program for
// Insertion in binary search tree by using recursion
class TreeNode
{
	public data: number;
	public left: TreeNode;
	public right: TreeNode;
	constructor(data: number)
	{
		this.data = data;
		this.left = null;
		this.right = null;
	}
}
class BinarySearchTree
{
	public root: TreeNode;
	constructor()
	{
		this.root = null;
	}
	// Insert a node element
	public TreeNode addNode(node: TreeNode, data: number)
	{
		if (node != null)
		{
			if (node.data >= data)
			{
				// When new element is smaller or
				// equal to current node
				node.left = this.addNode(node.left, data);
			}
			else
			{
				// When new element is higher to current node
				node.right = this.addNode(node.right, data);
			}
			// important to manage root node
			return node;
		}
		else
		{
			return new TreeNode(data);
		}
	}
	// Display preorder
	public preorder(node: TreeNode)
	{
		if (node != null)
		{
			// Display node value
			console.log("  " + node.data);
			// Visit to left subtree
			this.preorder(node.left);
			// Visit to right subtree
			this.preorder(node.right);
		}
	}
	public inorder(node: TreeNode)
	{
		if (node != null)
		{
			// Visit to left subtree
			this.inorder(node.left);
			// Display node value
			console.log("  " + node.data);
			// Visit to right subtree
			this.inorder(node.right);
		}
	}
	public postorder(node: TreeNode)
	{
		if (node != null)
		{
			// Visit to left subtree
			this.postorder(node.left);
			// Visit to right subtree
			this.postorder(node.right);
			// Display node value
			console.log("  " + node.data);
		}
	}
	public static main(args: string[])
	{
		var tree = new BinarySearchTree();
		/*
		         10
		        / \
		       /   \
		      4     15
		     / \   /
		    3   5 12
		    -------------
		    Build binary search tree


		*/
		tree.root = tree.addNode(tree.root, 10);
		tree.addNode(tree.root, 4);
		tree.addNode(tree.root, 3);
		tree.addNode(tree.root, 5);
		tree.addNode(tree.root, 15);
		tree.addNode(tree.root, 12);
		// Display tree nodes
		console.log("Preorder ");
		tree.preorder(tree.root);
		console.log("\nInorder ");
		tree.inorder(tree.root);
		console.log("\nPostorder ");
		tree.postorder(tree.root);
	}
}
BinarySearchTree.main([]);
/*
 file : code.ts
 tsc --target es6 code.ts
 node code.js
 */

Output

Preorder
  10
  4
  3
  5
  15
  12

Inorder
  3
  4
  5
  10
  12
  15

Postorder
  3
  5
  4
  12
  15
  10