Question How to create an inspector dropdown to conceal fields

I have lots of fields in some of my inherited classes and I was looking for something like this to hide/show fields. I've seen threads about using a CustomEditor but the threads I've seen aren't really what I'm looking for.

 

You can do want you want with a Foldout https://docs.unity3d.com/ScriptReference/EditorGUILayout.Foldout.html