如何在WPF中的DataTemplate中访问根DataContext？

<DataTemplate x:Key="MyDataTemplate">
    <TextBlock>
        <TextBlock.Text>
           <MultiBinding StringFormat="{}{0} - {1}">
               <Binding Path="Property1" />
               <Binding RelativeSource="{RelativeSource AncestorType=Window}" Path="DataContext.Property2" />
            </MultiBinding>
        </TextBlock.Text>
    </TextBlock>
</DataTemplate>

        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:MyApp"
        Title="MainWindow"
        DataContext="{Binding RelativeSource={RelativeSource Self}}">

   <Window.Resources>
       <local:MyViewModel x:Key="MyViewModel" />
    </Window.Resources>

   <ContentControl ContentTemplate="{StaticResource MyDataTemplate}"
                    Content="{Binding Source={StaticResource MyViewModel}}" />
</Window>