Service trees run at a user level, they are activated (initialized) after a user logs in to the account.
All the 66 tools react in the same manner as the root user. You just need to call the command with your regular user instead of the root user.
For example to create a tree and enable dbus-session@ service, you need to do so as a regular user (replace <mytree> by the name that you want to use, and replace <myuser> by the name of your user):
% 66-tree -cnE <mytree>
% 66-enable dbus-session@<myuser>
As you can see this is exactly the same procedure as root user.
Before a user can create and initialize user trees and services the sys-admin (root) must have initiated the ability for s6 to supervise thoses tasks. To see how this is done please see the document on boot-user@<username> module.