Do not touch it till next summer after the new growth has pushed out and opened. Next year. The quickest way to kill a collected tree is to mess around with it too soon after collecting expecially if it is old. Besides; what if you checked and there were no roots??? What do you think you would do??
Hmmm if it was potted in August , is that early fall up in Wisc? Definitely needs winter shelter , maybe even a heat mat … you’ll forgo true dormancy in the roots for recovery but that won’t hurt it for one season..
Don't even bother checking. You still need to wait for a year or more to do anything else with the tree so there is no point in knowing any more now. Just continue care and keep your fingers crossed.
If you barely potted it in early August, it would do more harm if you mess around with it at the moment. Let it recover, and hopefully, you will see some new growth by spring time. Even then, it would still be early to lift it out of the container just to check the roots. the best indicator is healthy growth/recovery.