Xamarin.Forms is my go to technology for cross platform app development. I have been using it for over four years, and I have built several apps for iOS, Windows 10, and Android using it. My app Hardfolio is built with Xamarin.Forms. My portfolio consists of several Xamarin based cross platform libraries for USB access, cryptocurrency hardwarewallet access, REST client access, and more. If you need help with Xamarin, or Xamarin Forms, please fill out the contact form.
Here is an example of a TreeView component that I developed for Xamarin.Forms: