How to cause a process started in .xsessionrc to terminate with x-session termination?

[Arkadiusz Dabrowski]

Hi all
I have a problem with unison sync termination when it is started from
.xsessionrc.
It works flawlessly but when I log out it is orphaned and not terminated.
I start it like this:
nice -n18 ionice -c2 -n7 unison unison_profile &>/dev/null &
Once started the parent is x-session-manager and they the same process
group.
What can I do to terminate the process with x-session?