How to populate child nodes asynchronously in uwp treegrid?

About the example

This example illustrates how to populate child nodes asynchronously in uwp treegrid

Name		Name	Last commit message	Last commit date
Latest commit History 6 Commits
.github/workflows		.github/workflows
Assets		Assets
Properties		Properties
App.xaml		App.xaml
App.xaml.cs		App.xaml.cs
App1.csproj		App1.csproj
App1.csproj.user		App1.csproj.user
App1.sln		App1.sln
App1Error2018-08-28.log		App1Error2018-08-28.log
App1_TemporaryKey.pfx		App1_TemporaryKey.pfx
MainPage.xaml		MainPage.xaml
MainPage.xaml.cs		MainPage.xaml.cs
Model.cs		Model.cs
Package.appxmanifest		Package.appxmanifest
README.md		README.md
ViewModel.cs		ViewModel.cs
project.json		project.json
project.lock.json		project.lock.json