Top view of binary tree using recursion in scala

Scala program for Top view of binary tree using recursion. Here problem description and explanation.

/* 
  Scala program for
  Top view of binary tree using dfs
*/
// 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,
	var level: Int)
{
	def this()
	{
		this(null, 0);
	}
	// Print left side top nodes including root
	def printleftSide(node: TreeNode, depth: Int): Unit = {
		if (node != null)
		{
			if (this.level < depth)
			{
				// Print the resultant node
				print("  " + node.data);
				this.level = depth;
			}
			// Recursively
			// Visit left subtree
			printleftSide(node.left, depth + 1);
			// Visit right subtree
			printleftSide(node.right, depth - 1);
		}
	}
	// Print right side top nodes
	def printRightSide(node: TreeNode, depth: Int): Unit = {
		if (node != null)
		{
			if (this.level < depth)
			{
				// Print the resultant node
				print("  " + node.data);
				this.level = depth;
			}
			// Recursively
			// First visit right subtree
			printRightSide(node.right, depth + 1);
			// Then
			// Visit left subtree
			printRightSide(node.left, depth - 1);
		}
	}
	// This is handle the request of printing top view
	def topView(): Unit = {
		this.level = -1;
		printleftSide(this.root, 0);
		this.level = 0;
		printRightSide(this.root, 0);
	}
}
object Main
{
	def main(args: Array[String]): Unit = {
		// Create new tree
		var tree: BinaryTree = new BinaryTree();
		/*
		   Make A Binary Tree
		-----------------------
		         1
		       /   \
		      2     3
		     /     / \
		    4     5   6
		   /       \    
		  7         8    
		             \
		              9
		               \
		                10
		*/
		// Construct binary tree
		tree.root = new TreeNode(1);
		tree.root.left = new TreeNode(2);
		tree.root.right = new TreeNode(3);
		tree.root.right.right = new TreeNode(6);
		tree.root.right.left = new TreeNode(5);
		tree.root.left.left = new TreeNode(4);
		tree.root.left.left.left = new TreeNode(7);
		tree.root.right.left.right = new TreeNode(8);
		tree.root.right.left.right.right = new TreeNode(9);
		tree.root.right.left.right.right.right = new TreeNode(10);
		// Display top view
		tree.topView();
	}
}

Output

  1  2  4  7  3  6  10