Filtering an Observable Collection in WPF MVVM via ICollectionView

public ObservableCollection<GistViewModel> Gists { get => gists; set => SetProperty(ref gists, value); }

public BindingList<GistFileViewModel> GistFiles { get => gistFiles; }

<!-- GistLevel -->
<HierarchicalDataTemplate DataType="{x:Type viewmodels:GistViewModel}" ItemsSource="{Binding Path=GistsFiles}">

    <StackPanel Orientation="Horizontal">
        <TextBlock Text="{Binding GistFiles, Converter={StaticResource GistFilesToFirstFilenameConverter}}"></TextBlock>
    </StackPanel>
    
</HierarchicalDataTemplate>

<!-- GIST FILE LEVEL -->

<DataTemplate DataType="{x:Type viewmodels:GistFileViewModel}">
    <StackPanel Orientation="Horizontal">
        <TextBlock  VerticalAlignment="Center" Margin="2,0,2,0" Text="{Binding Filename}"></TextBlock>
    </StackPanel>
</DataTemplate>

<TreeView x:Name="GistsTV" ItemsSource="{Binding Gists}"/>

public ICollectionView GistsView { get => CollectionViewSource.GetDefaultView(Gists); }

private async Task GetAllGistsAsync()
{    
    Gists = await gistManager.LoadGistsAsync();
    GistsView.Refresh();
}

<TreeView x:Name="GistsTV" ItemsSource="{Binding GistsView}"/>