我创建了渐变背景，现在场景中的所有按钮都不可见

Question

我创建了渐变背景，现在我以前拥有的所有按钮都不可见。但是按钮仍然存在，因为如果我触摸例如播放按钮所在的区域，控制台将打印：“按下播放按钮”。如何使按钮再次可见？

代码：

import UIKit
import SpriteKit
import StoreKit
import GameKit
import AVFoundation
import SpriteKit.SKTexture


class Start: SKScene {


//Button
let settingButton = SKSpriteNode(imageNamed: "Settings")
let playButton = SKSpriteNode(imageNamed: "NewGame")


 //Background

func makeGradientColor(`for` object : AnyObject , startPoint : CGPoint , endPoint : CGPoint) -> CAGradientLayer {
    let gradient: CAGradientLayer = CAGradientLayer()

    gradient.colors = [(UIColor(red: 12/255.0, green: 121/255.0, blue: 208/255.0, alpha: 1.00).cgColor), (UIColor(red: 85/255.0, green: 229/255.0, blue: 254/255.0, alpha: 1.00).cgColor)]
    gradient.locations = [0.0 , 1.0]

    gradient.startPoint = startPoint
    gradient.endPoint = endPoint
    gradient.frame = CGRect(x: 0.0, y: 0.0, width: object.frame.size.width, height: object.frame.size.height)
    return gradient
}

override func didMove(to view: SKView) {

    //Background
    let start1 : CGPoint = CGPoint(x: 1.0, y: 1.0)
    let end1 : CGPoint = CGPoint(x: 1.0, y: 0.0)
    let gradient1: CAGradientLayer = self.makeGradientColor(for: (self.view ?? nil)!, startPoint: start1, endPoint: end1)
    self.view?.layer.insertSublayer(gradient1, at: 0)

    //Button
    playButton.setScale(0.6)
    playButton.zPosition = 1
    playButton.position = CGPoint(x: self.size.width / 2, y: self.size.height * 0.4)
    self.addChild(playButton)

    settingButton.setScale(0.4)
    settingButton.zPosition = 1
    settingButton.position = CGPoint(x: self.size.width * 0.9, y: self.size.height * 0.94)
    self.addChild(settingButton)
  }
}