Inorder traversal of binary tree with recursion in swift

Swift program for Inorder traversal of binary tree with recursion. Here problem description and explanation.

import Foundation
/* 
  Swift 4 Program for
  inorder tree traversal of a Binary Tree
  using recursion
*/
// 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? ;
	init()
	{
		self.root = nil;
	}
	// Display Inorder view of binary tree
	func inorder(_ node: TreeNode? )
	{
		if (node  != nil)
		{
			// Visit left subtree
			self.inorder(node!.left);
			//Print node value
			print(node!.data, terminator: "  ");
			// Visit right subtree
			self.inorder(node!.right);
		}
	}
	static func main(_ args: [String])
	{
		// Create new tree
		let tree: BinaryTree? = BinaryTree();
		/*
		    Make A Binary Tree
		    ----------------
		        15
		       /  \
		      24   54
		     /    /  \
		    35   62   13
		*/
		// Add tree TreeNode
		tree!.root = TreeNode(15);
		tree!.root!.left = TreeNode(24);
		tree!.root!.right = TreeNode(54);
		tree!.root!.right!.right = TreeNode(13);
		tree!.root!.right!.left = TreeNode(62);
		tree!.root!.left!.left = TreeNode(35);
		// Display Tree Node
		tree!.inorder(tree!.root);
	}
}
BinaryTree.main([String]());

Output

35  24  15  62  54  13