<HierarchicalDataTemplate
    x:Key="CheckBoxedTreeViewItem"
    ItemsSource="{Binding Path=SubItems}">
    <StackPanel Orientation="Horizontal">
      <CheckBox IsChecked="{Binding Path=Checked}"/>
      <TextBlock Text="{Binding Path=Text}"/>
    </StackPanel>
  </HierarchicalDataTemplate>

    <TreeView 
      ItemsSource="{Binding}"
      ItemTemplate="{StaticResource CheckBoxedTreeViewItem}"/>