How to create a custom hierarchical wpf TreeView

Hi,

I know there are many examples on the net but I cannot figure out how to achieve what I have to do.

My classes are:

public abstract class UIProperties : System.Object
{
  public abstract string Caption { get; }
  public abstract string Description { get; }
}

public class CMask : UIProperties
{
  ....
}

public class CommandBlock : UIProperties
{
  public CMask Mask { get; set; }
}

public class CButton: UIProperties
{
  public EButtonActions ButtonAction { get; set; }
  public ObservableCollection<CommandBlock> ButtonChain { get; set; }
}

The TreeView I want to create is:

+ CButton.Descriprion
        |
        |-- ButtonAction
        |
        |-- CommandBlock.Description
        |               |
        |               |-- Mask.Description
        |
        |-- CommandBlock.Description
                        |
                        |-- Mask.Description+ CButton.Descriprion
        |
        ...

I'm using this XAML (where Buttons is an ObservableCollection of CButton) but how can I handle the ButtonAction node and the situation when the CommandBlock::Mask is null?

<TreeView Name="tvButtons"
          ItemsSource="{Binding Buttons}" ><TreeView.Resources><HierarchicalDataTemplate DataType="{x:Type local:CButton}"
                              ItemsSource="{Binding Path=ButtonChain}"><TextBlock  Text="{Binding Path=Description}" /></HierarchicalDataTemplate><HierarchicalDataTemplate DataType="{x:Type local:CommandBlock}"><TextBlock Margin="2" Text="{Binding Path=Description}" /></HierarchicalDataTemplate><HierarchicalDataTemplate DataType="{x:Type local:CMask}"><TextBlock Margin="2" Text="{Binding Path=Description}" /></HierarchicalDataTemplate></TreeView.Resources></TreeView>

I cannot use code behind because this is a data template loaded at runtime into a tab control so it has no code associated.

Some suggestions?