Hi,
Thank you for posting in Symantec community.
I would be glad to answer your query.
can be automatic installation once the session login in windows is performed ?
--> It's not possible with the help of SEPM. If you selected an option " Notify users before an upgrade" can help but not the way you looking for. I mean it won't be 100% automatic.
Third party software's can help you to achieve this result.
Generally everybody expect that it should trigger when no one is logged in & they do schedule upgrade accordingly. Why do you want this to be happen after users logged in?