Yes, the blockage could still be there. It could be a 2nd blockage, and not related to the 1st one.
You need to consider having the 'cause of the problem' (the tree(s)) removed. Otherwise, the plumber will continue to return. What might happen next time is your basement may flood, you toilet may overflow, or your dishwasher may empty onto the kitchen floor. Be SURE your homeowners insurance has a rider on it for sewer damage. It is USUALLY a separate rider. ('Clean water' damage is usually part of the standard policy but DO check to be sure.) Also, some policies DON'T cover personal belongings in rooms such as unfinished basements, for either sewer damage, clean water damage, or both. Again, read the policy to be SURE.
The next time the plumber comes out and 'fixes' your problem, TEST each and EVERY appliance. Run your dishwasher, run your washer, fill your 'tub', fill your sinks, flush EVERY toilet, and so on. You MAY be able to argue w/him that he should have checked every 'line' that drains into the main. He may have fixed 1 problem but didn't have the foresight to do a more thorough fix. You can simply tell him the problem is still there. (I'd go w/that.) Just tell him, "Yea, you fixed the OBVIOUS problem but I still have a blockage. You assured me the problem was 'fixed' but it's not."
My best to ya and hope this helps.
Jay J -Moderator
PS: See if you can get an idea of where the problems (ALL of the roots) are located. You can then dig up those sections (and the area on both sides of the 'intrusions') and have them replaced. Yes, it will cost some good $$$. I do have to ask - Did you have a Home INspection? If so, did the Inspector flush any toilets or anything? Shouldn't he have found this problem? Check your paperwork to see if this 'test' was in his paperwork, and see what he wrote. IF you mentioned this during your walk-through, you shouldn't have to pay for the fix. (That's my opinion ...)
PPS: God Bless America!