What is the maximum level of Expand parameter for Content Areas?

We have a page strucutre with 3-4 levels of nested blocks inside of Content Areas. 
Simplified example :

public class Level2Block : BaseBlock
{
    public virtual string Name { get; set; }
    public virtual int Age { get; set; }
}
public class Level1Block : BaseBlock
{
    [AllowedTypes(typeof(Level2Block))]
    public virtual ContentArea Level2 { get; set; }
}
class MyPage : BasePage 
{
    [AllowedTypes(typeof(Level1Block))]
    public virtual ContentArea Level1 { get; set; }
}

The problem is that Content Delivery Api with expand=* will expand only Level1  property,

but Level2 property will not be expanded and will contain a list of content links to contained Level2 blocks.

Is there any solution or at least a reason of what is going on?