WPF: styling a HierarchicalDataTemplate
<Grid.Resources>
<HierarchicalDataTemplate ItemsSource="{Binding Items}" DataType="{x:Type entities:Folder}" ItemContainerStyle="{StaticResource FileComponentItem}">
    <Grid ShowGridLines="False" HorizontalAlignment="Center">
        <TextBlock Grid.Column="0" Text="{Binding Type}" />
    </Grid>
</HierarchicalDataTemplate>
<HierarchicalDataTemplate ...... />
</Grid.Resources>

<TreeView Grid.Row="1" BorderThickness="0" ItemsSource="{Binding}"  ItemContainerStyle="{StaticResource FlattenedTreeViewItem}"></TreeView>