or
<telerik:RadPanelBar x:Name="pnlTopic" HorizontalAlignment="Left" VerticalAlignment="Top" Orientation="Vertical" ExpandMode="Single" telerikQuickStart:ThemeAwareBackgroundBehavior.IsEnabled="True" ItemsSource="{Binding Topics}" SelectedItem="{Binding SelectedTopic}"> <telerik:RadPanelBar.ItemTemplate> <DataTemplate> <telerik:RadPanelBarItem Header="{Binding Name}" IsSelected="True" IsExpanded="{Binding DataContext.IsExpanded,ElementName=pnlTopic}" x:Name="pnliTopic" > <ListBox x:Name="lstSubTopics" ItemsSource="{Binding DataContext.SubTopics,ElementName=pnlTopic}"> <ListBox.ItemTemplate> <DataTemplate> <TextBlock Text="{Binding Name}" Margin="2" FontWeight="SemiBold" /> </DataTemplate> </ListBox.ItemTemplate> </ListBox> </telerik:RadPanelBarItem> </DataTemplate> </telerik:RadPanelBar.ItemTemplate> <i:Interaction.Triggers> <i:EventTrigger EventName="SelectionChanged"> <i:InvokeCommandAction Command="{Binding AccordionSelectionChange}" CommandParameter="{Binding Item}"/> </i:EventTrigger> </i:Interaction.Triggers> </telerik:RadPanelBar>