I can't give you advice, as I am just some random nutter on the internet. But I can share my experience which is that for me it is absolutely NOT the case that diabetes works out like that maths-wise. If my basal is slightly short I can need to add units and units of insulin in corrections, but when I finally basal test and cautiously adjust my background dose I need to add a very small amount spread over the day.
In your shoes I would first do a fasting basal test to ensure that it actually WAS my basal that was adrift. And then adjust by something like 10% of my dose if it seemed an adjustment was necessary. Leave that a couple of days... recheck... repeat... and so on.
There's a helpful guide to basal testing here
http://www.diabetes-support.org.uk/info/?page_id=120.
As others have said you do need to be cautious especially with a flat-ish profile insulin like Tresiba, because your requirements through the day might be varied. And you risk your basal over-reaching your needs of you push it up too high, which will more than likely give you a ton of hypos.
Good luck with it!