You have the possibility of defining main sessions to sub-sessions.
To do this, go to "Sessions" the relevant sub-session tab 5 "Sessions"
Click on "Create a new link".
Give a name to your main session, as well as to the sub-session, and click on "Add":
Select the hierarchical level of the session you want to link, then search for it and select it in the drop-down list:
Here, the "Break" session is well displayed as a sub-session of the opening session: