Binding a TreeView to a large dataset.

I have a large XML document that I'm binding to a TreeView for testing
purposes. There are relatively few nodes at depth=1 so the tree is
displayed quickly. However there are a lot of nodes at depth=2 (200-300
per depth=1 node) and expanding the closed depth=1 nodes causes the UI
to freeze whilst the binding occurs.

As the freeze happens when I try to expand the node, I'm assuming that
the TreeView is 'lazy' binding to the XML data.

Here is the XAML (I'm setting the DataContext of the TreeView in code) :

<HierarchicalDataTemplate DataType="section"
ItemsSource="{Binding XPath=section}">
<TextBlock Text="{Binding XPath=@description}"/>
</HierarchicalDataTemplate>

<TreeView Name="_sectionTree"
ItemsSource="{Binding XPath=/sites/section}"
BorderThickness ="0">

I have a few questions.

1) Is it the binding that is freezing the UI?
2) Is there a better way to perform the binding so that the UI does not
freeze?
3) If not, are there any events that I can handle do give user feedback
before and after the binding occurs? i.e. change the cursor or display
a 'loading...' node.

Cheers

Tom.

Tom,
I'm having a similar problem. I've got a ListBox templated with a
HierarchicalDataTemplate. When I bind a couple of hundred items to the list
it freezes up the UI, and when I un-bind those and bind a smaller subset, it
takes just as long. However going from one small list of items to another
small list of items, it does not freeze up the UI.

Can anyone shed some light on this?