How to add gradient to ASDisplayNode or ASButtonNode

I am looking to add a gradient background to an ASDisplayNode/ASButtonNode. I have tried creating a gradient layer and adding it as a sublayer like this -

CAGradientLayer *gradient = [CAGradientLayer layer];
gradient.frame = button.frame;
gradient.colors = @[[UIColor redColor], [UIColor blueColor]];
[button.view.layer insertSublayer:gradient atIndex:0];

where button is of type ASButtonNode, but this just gives a white background to the button. I haven't been able to find much documentation for achieving this either.

How can I go about adding a background given an array of UIColor and a CGFloat angle?

Thanks

Swift 3.

extension UIView {

       func gradient(color1: UIColor, color2: UIColor) -> CAGradientLayer {
             let gradient: CAGradientLayer = CAGradientLayer()
             gradient.colors = [color1.cgColor, color2.cgColor]
             gradient.locations = [0.0 , 1.0]
             gradient.startPoint = CGPoint(x: 0.0, y: 0.0)
             gradient.endPoint = CGPoint(x: 1.0, y: 1.0)
             gradient.frame = CGRect(x: 0.0, y: 0.0, width: frame.size.width, height: frame.size.height)
             return gradient
          } 
    }

Example:

let gradient = self.cardGradientNode.view.gradient(
    color1: gradient.start, 
    color2: gradient.end
)
self.cardGradientNode.view.layer.insertSublayer(gradient, at: 0)

Result: