I am creating a web-site on wordpress platform where I want to be able to post my own book texts. So what I want is to have a some kind of hierarchy where I would add a post
Posts in Wordpress are supposed to be typical chronological Blog Posts. Pages are made for static content, they can be organised in a hierarchical structure out of the box.
For any Page, you can select a parent page. This way, you can create nested hierarchies with multiple children. Sounds like what you need.
Check the Wordpress Documentation for details.
If you have a deep, complicated tree structure, a plugin might help you manage it, like Wordpress Page Tree. It provides a better interface than the default Wordpress Page listing.