How do I make a Dropdown of items in my custom editor window like how the Project window shows all the folders/files

I’m currently trying to get my custom editor window display a list of items and would like it to look like and basically function the same as the Project window. I’ve found a unity manual page about it but it doesn’t seem to show how to access it in a script.

So I am actuially looking for something similar. You can Manage a “dropdown list” using EditorGUILayout.Foldout(). Such Dropdown lists are called foldout. This should give you a starting point. I am actually looking for the Buttons (Button Styles) you have in the Hierarchy. I cannot understand why such basic selection style is so hard to find (or even not available for custom GUI). If you find something about this please let me know!!