swift background image for all viewcontrollers : i would like to swift background image for all viewcontrollers, 
please kind help to adv. how to do it. the below code is work for a single viewcontroller.

    let backgroundImage = UIImageView(frame: UIScreen.main.bounds)
    backgroundImage.image = UIImage(named: "bg_name.png")
    backgroundImage.contentMode = UIViewContentMode.scaleAspectFill
    self.view.insertSubview(backgroundImage, at: 0)