Convert binary tree to mirror tree in scala

Scala program for Convert binary tree to mirror tree. Here problem description and explanation.

/* 
  Scala program for
  Convert binary tree to it's mirror tree
*/
// Binary Tree Node
class TreeNode(var data: Int,
	var left: TreeNode,
		var right: TreeNode)
{
	def this(data: Int)
	{
		// Set node value
		this(data, null, null);
	}
}
class BinaryTree(var root: TreeNode)
{
	def this()
	{
		this(null);
	}
	// Display inorder element
	def inorder(node: TreeNode): Unit = {
		if (node != null)
		{
			inorder(node.left);
			// Print node value
			print("  " + node.data);
			inorder(node.right);
		}
	}
	// Convert binary tree into mirror tree
	def mirrorTree(node: TreeNode): Unit = {
		if (node != null)
		{
			mirrorTree(node.left);
			mirrorTree(node.right);
			// Change left and right child
			var temp: TreeNode = node.left;
			node.left = node.right;
			node.right = temp;
		}
	}
}
object Main
{
	def main(args: Array[String]): Unit = {
		// Create new tree
		var tree: BinaryTree = new BinaryTree();
		/*
		   Binary Tree
		    -----------------------
		         1
		       /   \
		      6     8
		     / \   / \
		    2   3 4   5
		   /           \
		  19            10
		            
		*/
		// Add element
		tree.root = new TreeNode(1);
		tree.root.left = new TreeNode(6);
		tree.root.left.left = new TreeNode(2);
		tree.root.right = new TreeNode(8);
		tree.root.right.right = new TreeNode(5);
		tree.root.right.left = new TreeNode(4);
		tree.root.left.right = new TreeNode(3);
		tree.root.left.left.left = new TreeNode(19);
		tree.root.right.right.right = new TreeNode(10);
		print("\n Before convert");
		print("\n In-order Data : ");
		tree.inorder(tree.root);
		// Transform into mirror tree
		tree.mirrorTree(tree.root);
		/*
		    Mirror Tree
		    --------------
		         1
		       /   \
		      8     6
		     / \   / \
		    5   4 3   2
		   /           \
		  10            19
		             
		*/
		print("\n After convert");
		print("\n In-order Data : ");
		tree.inorder(tree.root);
	}
}

Output

 Before convert
 In-order Data :   19  2  6  3  1  4  8  5  10
 After convert
 In-order Data :   10  5  8  4  1  3  6  2  19