WPF DataTrigger on ViewModel Property Change

I'm trying to fire a trigger when a property in my ViewModel changes. I can't seem to get the trigger to fire no matter what I try. My XAML looks like this:

<TreeView.ItemContainerStyle>
<Style TargetType="{x:Type TreeViewItem}">
    <Setter Property="IsExpanded" Value="{Binding IsExpanded, Mode=TwoWay}" />
    <Setter Property="IsSelected" Value="{Binding IsSelected, Mode=TwoWay}" />
    <Setter Property="Padding" Value="0 1" />
    <Setter Property="FontWeight" Value="Normal" />
    <Style.Triggers>
        <DataTrigger Binding="{Binding IsExpanding}" Value="True">
            <Setter Property="Control.Template" Value="{StaticResource ResourceKey=loadingTreeViewItem}" />
        </DataTrigger >
        <Trigger Property="IsSelected" Value="True">
            <Setter Property="FontWeight" Value="Bold" />                            
        </Trigger>
    </Style.Triggers>
</Style>

The IsExpanded and IsSelected bindings are working fine, however I can't get the DataTrigger to fire when IsExpanding is true. These properties are in the same ViewModel. I have tried adding different variations for RelativeSource but am not having any luck. Any 开发者_开发知识库feedback is appreciated.

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Turns out the trigger was working. The problem was that the IsExpanding property and the call to get the data for the TreeView were both happening on the UI thread. I threaded the call to get the data and everything is working as expected