Top view of binary tree using recursion in swift

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

import Foundation
/* 
  Swift 4 program for
  Top view of binary tree using dfs
*/
// Binary Tree Node
class TreeNode
{
	var data: Int;
	var left: TreeNode? ;
	var right: TreeNode? ;
	init(_ data: Int)
	{
		// Set node value
		self.data = data;
		self.left = nil;
		self.right = nil;
	}
}
class BinaryTree
{
	var root: TreeNode? ;
	var level: Int;
	init()
	{
		self.root = nil;
		self.level = 0;
	}
	// Print left side top nodes including root
	func printleftSide(_ node: TreeNode? , _ depth : Int)
	{
		if (node  != nil)
		{
			if (self.level < depth)
			{
				// Print the resultant node
				print(node!.data, terminator: "  ");
				self.level = depth;
			}
			// Recursively
			// Visit left subtree
			self.printleftSide(node!.left, depth + 1);
			// Visit right subtree
			self.printleftSide(node!.right, depth - 1);
		}
	}
	// Print right side top nodes
	func printRightSide(_ node: TreeNode? , _ depth : Int)
	{
		if (node  != nil)
		{
			if (self.level < depth)
			{
				// Print the resultant node
				print(node!.data, terminator: "  ");
				self.level = depth;
			}
			// Recursively
			// First visit right subtree
			self.printRightSide(node!.right, depth + 1);
			// Then
			// Visit left subtree
			self.printRightSide(node!.left, depth - 1);
		}
	}
	// This is handle the request of printing top view
	func topView()
	{
		self.level = -1;
		self.printleftSide(self.root, 0);
		self.level = 0;
		self.printRightSide(self.root, 0);
	}
	static func main(_ args: [String])
	{
		// Create new tree
		let tree: BinaryTree? = BinaryTree();
		/*
		   Make A Binary Tree
		-----------------------
		         1
		       /   \
		      2     3
		     /     / \
		    4     5   6
		   /       \    
		  7         8    
		             \
		              9
		               \
		                10
		*/
		// Construct binary tree
		tree!.root = TreeNode(1);
		tree!.root!.left = TreeNode(2);
		tree!.root!.right = TreeNode(3);
		tree!.root!.right!.right = TreeNode(6);
		tree!.root!.right!.left = TreeNode(5);
		tree!.root!.left!.left = TreeNode(4);
		tree!.root!.left!.left!.left = TreeNode(7);
		tree!.root!.right!.left!.right = TreeNode(8);
		tree!.root!.right!.left!.right!.right = TreeNode(9);
		tree!.root!.right!.left!.right!.right!.right = TreeNode(10);
		// Display top view
		tree!.topView();
	}
}
BinaryTree.main([String]());

Output

1  2  4  7  3  6  10