How do I sort a WPF treeview that has items bound to the properties of an Item subclass?

I have two classes,

public class BookItem
{
    public string BookID            { get; set; }
    public string ItemID            { get; set; }
    public Item Item                { get; set; }   
    public ItemType Type            { get; set; }
    public string ParentID          { get; set; }
    public string BoxID             { get; set; }
    public string StyleID           { get; set; }
    public string NotesID           { get; set; }
    public string Code_XAML         { get; set; }
    public string Description_XAML      { get; set; }
    public CompositeCollection SubItems { get; set; }
}

public class Item : ClaunchBaseClass
{
    public string ItemID        { get; set; }
    public int    Type          { get; set; }
    public string Code          { get; set; }
    public string Description   { get; set; }
    private BookList _books = new BookList();
    public BookList Books       { get {return _books;} set { _books = value; }}
}

and I've created the following XAML:

<pre>    
<TreeView Name="tvList" Grid.Row="2" MouseDoubleClick="tvList_MouseDoubleClick">
    <TreeView.ItemTemplate>
        <HierarchicalDataTemplate DataType="x:Type j:BookItem" ItemsSource="{Binding SubMenu}">
            <Grid>
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="50"/>
                    <ColumnDefinition Width="*"/>
                </Grid.ColumnDefinitions>
                <TextBlock Text="{Binding Item.Code}" Grid.Column="0" />
                <TextBlock Text="{Binding Item.Description}" Grid.Column="1"/>
            </Grid>
        </HierarchicalDataTemplate>
    </TreeView.ItemTemplate>
</TreeView>
<code>

This XAML binds the treeview items to the collection of book items and displays the Item subclass's Description and Code, the treeview populates and displays correctly but now I want to sort the treeview on either Item.Code or Item.Description and have tried the following with no results:

<pre> 
var bookItemsSort = CollectionViewSource.GetDefaultView(_bookItemList) as ListCollectionView;
tvList.ItemsSource = _bookItemList;         //bind the book items to the treeview
bookItemsSort.SortDescriptions.Clear();
bookItemsSort.SortDescriptions.Add(new SortDescription(sort, Ascending));
<code>

I've had this code work correctly for other treeviews so I can only guess it is a problem with binding to a subclass.

Jeremy

While the answers here provided partial answers to my question, none of them gave the answer that I needed.

The most sensible solution for this problem was to write my own object comparer for this object type and sort the underlying list and then re-bind the new list to the treeview. This allowed for comparing sublasses at any nested level which I couldn't make work any other way :)

You need to get the default view for each sub-list, and apply a CollectionViewSource sorting to it. The code you posted only affects the top level items.

Bind your TreeView.ItemsSource to the DefaultView. SortDescriptions will not change your DataList, only the View of it.