Nested routes in ember engine routes.js?

How to define nested routes in ember routable engine? I can't navigate to beyond 2 trees. Like, For example

All posts
 Post
   Comments
     Comment

I can access

localhost:4200/posts/:postid/

But when I access

localhost:4200/posts/:postid/comments/:commentid

Its not rendering the content for comments template. But it doesn't show any error either.