Two Generic List in one Type

I would like to style generic variables with XAML. For that I need {x:Type myTypes:theType}.

So I have:

public class BaseClass
{
    //
}

public class ClassA : BaseClass
{
    //
}

public class ClassB : BaseClass
{
    //
}

public class ListA : List<ClassA>
{
    //
}

public class ListB : List<ClassB>
{
    //
}

Is it possible that I create a class that can be eather ListA or ListB?

Thank you!