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

[dpaulino]

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.

[ghost]

Hello dpaulino, thank you for opening an issue with us!

I have automatically added a "needs triage" label to help get things started. Our team will analyze and investigate the issue, and escalate it to the relevant team if possible. Other community members may also look into the issue and provide feedback 🙌