I'm attaching you an example that I hope will help you. SampleViewModel class extends ObservableCollection and is used to provide data to the treeview.
If your model is more complex you can nest the ObservableCollection as a member of the ViewModel class. Then your ViewModel class must implement the INotifyPropertyChanged interface and fire the PropertyChanged event when changes are made to the ObservableCollection member. I left several comments in the sampleViewModel.cs file highlighting the milestones that must be performed when using ObservableCollection as a member.
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