Sum of all right leaf nodes of binary tree in typescript

Ts program for Sum of all right leaf nodes of binary tree. Here mentioned other language solution.

/*
    TypeScript program for
    Sum of all right leaves nodes in a binary tree
    Using recursion
*/
// Binary Tree node
class TreeNode
{
	public data: number;
	public left: TreeNode;
	public right: TreeNode;
	constructor(data: number)
	{
		// Set node value
		this.data = data;
		this.left = null;
		this.right = null;
	}
}
class BinaryTree
{
	public root: TreeNode;
	constructor()
	{
		// Set initial tree root
		this.root = null;
	}
	// Display pre order elements
	public preorder(node: TreeNode)
	{
		if (node != null)
		{
			// Print node value
			console.log("  " + node.data);
			this.preorder(node.left);
			this.preorder(node.right);
		}
	}
	// Returns the Sum of all the right leaves in binary tree
	public number rightLeavesSum(node: TreeNode)
	{
		var sum = 0;
		if (node != null)
		{
			if (node.right != null && 
                node.right.left == null && 
                node.right.right == null)
			{
				// When get right leaf node
				sum = node.right.data;
			}
			// Recursively visit left and right subtree.
			// And find sum of right leaf nodes
			sum = sum + this.rightLeavesSum(node.left) + 
              this.rightLeavesSum(node.right);
		}
		return sum;
	}
	public static main()
	{
		// New binary tree
		var tree = new BinaryTree();
		/*
		    Constructor binary tree
		    -----------------------
		          6
		         / \ 
		        /   \                             
		       /     \    
		      2       3     
		     / \       \               
		    8   10      1
		       /  \    / \
		      6   -2  4   5
		*/
		// Add tree node
		tree.root = new TreeNode(6);
		tree.root.left = new TreeNode(2);
		tree.root.left.left = new TreeNode(8);
		tree.root.left.right = new TreeNode(10);
		tree.root.left.right.right = new TreeNode(-2);
		tree.root.left.right.left = new TreeNode(6);
		tree.root.right = new TreeNode(3);
		tree.root.right.right = new TreeNode(1);
		tree.root.right.right.left = new TreeNode(4);
		tree.root.right.right.right = new TreeNode(5);
		console.log("\n Tree Nodes : ");
		tree.preorder(tree.root);
		// Find right leaf sum
		var sum = tree.rightLeavesSum(tree.root);
		// Display result
		console.log("\n Right leaves nodes sum : " + sum);
	}
}
BinaryTree.main();
/*
 file : code.ts
 tsc --target es6 code.ts
 node code.js
 */

Output

 Tree Nodes :
  6
  2
  8
  10
  6
  -2
  3
  1
  4
  5

 Right leaves nodes sum : 3