Strategy to keep TreeView ViewModel and model in sync in C# WPF MVVM

Question

I try to keep a TreeView in sync with my data layer during drag-drop operations.

Questions

1. Should operations in the TreeView like drag-and-drop act on the ItemViewModel or should these be send to the service/data layer and then update the ItemViewModel?
2. I currently have two Tree structures, one in my data layer and one in my view layer. With regard to question 1 is this the proper way to do this?

Answer 1

I found the TreeListBox example in https://github.com/PropertyTools/PropertyTools/tree/develop/Source/Examples/TreeListBox a helpful example. It has separation between model and viewmodel and dragdrop/delete functions while keeping model in sync