UMG expandable tree structure

Hi all,

I am trying to make a expandable tree structure in UE4. The design is like the attached image.
I assumed I should use “Tree View” to make it.
However, I couldn’t find any tutorial regarding about the Tree View in UMG.
I dragged it onto a canvas, but it says “There is no EntryWidgetClass specified on this list. Even if doing custom stuff, this is always required as a fallback.”
I don’t even understand what’s a entry widget class.
When I googled it, there is no tutorial or documentation elaborating on this topic.
All I could find is a plug-in.
Is there any ways I can make a expandable tree structure in UMG?
Please help. I have been desperately trying to figure this out for days.