WPF Control Template Trigger, how to reference sub object

Question

I have AnswerContainer class which is inherited from ContentControl. The AnswerContainer has a public dependency property called Answer.

public class AnswerContainer : ContentControl
{
    public static DependencyProperty AnswerProperty;
    public Answer Answer
    {
    ...

Answer property is of type Answer and has a public dependency property IsSelected

public class Answer : DependencyObject 
{
    public static DependencyProperty IsSelectedProperty;
    public bool IsSelected
    {

I am making a default control style and template for the AnswerContainer. I need to create Trigger that is referencing AnswerContainer.Answer.IsSelected property but I am not sure how to do this. I have tried with the following code but compiler does not recognize my property:

<Trigger SourceName="Answer" Property="IsSelected" Value="True">

Any help on how to do this would be nice!