Prototype of a macOS App embedding Unity into an Xcode project

I want to extend an existing macOS Application developed in Xcode about a view (e.g. a subclass of 'NSView') presenting 3D-models using the Unity 3D engine. Writing the whole application in Unity doesn't work for me, so I need to find a way of embedding Unity to my Xcode-project. There must also be a possibility for my Swift-Code (Objective-C would also do) to control Unity and to load models into it. What I need is just the prototype of a native Mac Project created by Xcode displaying a window with a view containing the content of Unity. The view can do anything, e.g. just loading and displaying a static 3D-model, but it must demonstrate a way to control Unity from my native code. It's not necessary that the app looks nice or is free of bugs, I just need a proof of concept and the source code demonstrating me how to get started.