[Bug] AdvancedCollectionView sorting a WinUI TreeView seems to cancel tree node re-orderings

Describe the bug

When using an AdvancedCollectionView as the item source for a WinUI TreeView, any changes in the node structure of the tree seems to be reversed or canceled by a sort.

• Is this bug a regression in the toolkit? If so, what toolkit version did you last see it work:

Steps to Reproduce

Steps to reproduce the behavior:

1. Clone this repo: https://github.com/dpaulino/tree-sort-issue
2. Launch the app
3. Drag the "hello" node into the "world" node such that "hello" becomes a child of "world"
4. Click the A-Z sort button.
5. The tree structure gets reset such that "hello" is no longer a child.

Expected behavior

I expect the sort to:

• not modify the tree view nodes
• perform the sort only on the root node list of the tree

Screenshots

Video of the bug: https://1drv.ms/v/s!Ar4RhL72OhUDzroWOtjVcYQgEFWGbw?e=kWWWF8

Environment

NuGet Package(s): 
- Microsoft.Toolkit.Uwp.UI 6.0.0
- Microsoft.UI.Xaml 2.3.200213001

Package Version(s): 
- Microsoft.Toolkit.Uwp.UI 6.0.0
Windows 10 Build Number:
- [ ] Fall Creators Update (16299)
- [ ] April 2018 Update (17134)
- [ ] October 2018 Update (17763)
- [ ] May 2019 Update (18362)
- [x] Insider Build (build number: 19041.208)

App min and target version:
- [ ] Fall Creators Update (16299)
- [min] April 2018 Update (17134)
- [ ] October 2018 Update (17763)
- [target] May 2019 Update (18362)
- [ ] Insider Build (xxxxx)

Device form factor:
- [x ] Desktop
- [ ] Xbox
- [ ] Surface Hub
- [ ] IoT

Visual Studio 
- [ ] 2017 (version: )
- [x ] 2019 (version: 16.5.2) 
- [ ] 2019 Preview (version: )

Additional context

Add any other context about the problem here.