is there hierarchical user level structure in drupal Is there any hierachical structure of user in Drupal?
I just see user role in drupal, but can we define some level of user?
As example:

user1
--user2
---user3
--user4
---user5
---user6
Check out Subuser module to see if it fits your needs.

If you want "just" the roles to be hierarchical, Role delegation might be useful

Related: https://stackoverflow.com/questions/1281964/drupal-for-users-creating-sub-users