Insertion in a Binary tree

BinaryTreeInsertion.swift

import UIKit
import PlaygroundSupport

class TreeNode {
  var data: Int
  var left: TreeNode?
  var right: TreeNode?
  
  init(data: Int) {
    self.data = data
  }
}

class BinaryTree {
  var root: TreeNode
  
  init(root: TreeNode) {
    self.root = root
  }
      
  /// breadth first traversal
  func levelOrderTraversal() -> [Int] {
    var result = [Int]()
    var queue = [TreeNode?]()
    queue.append(root)
    while !queue.isEmpty {
      guard let node = queue.removeFirst() else { continue }
      result.append(node.data)
      queue.append(node.left)
      queue.append(node.right)
    }
    return result
  }
  
  func insertInLevelOrder(newNode: TreeNode) {
    var queue = [TreeNode?]()
    queue.append(root)
    while !queue.isEmpty {
      guard let node = queue.removeFirst() else { continue }
      if (node.left != nil) && (node.right != nil) {
        queue.append(node.left)
        queue.append(node.right)
      } else {
        if (node.right == nil) {
          node.right = newNode
        } else {
          node.left = newNode
        }
        return
      }
    }
  }
}

let node10 = TreeNode(data: 10)
let node11 = TreeNode(data: 11)
let node9 = TreeNode(data: 9)
let node7 = TreeNode(data: 7)
let node15 = TreeNode(data: 15)
let node8 = TreeNode(data: 8)

node10.left = node11
node10.right = node9
node11.left = node7
node9.left = node15
node9.right = node8

let tree = BinaryTree(root: node10)
print("levelOrder: ", tree.levelOrderTraversal())

tree.insertInLevelOrder(newNode: TreeNode(data: 12))
print("levelOrder after insertion: ", tree.levelOrderTraversal())