Maiden69
Masterpiece
I heard oaks are notorious for their tap roots but that's an overkill
I know I am late, but definitely the way to go... my cork oak still had the tap root, it was THICKER than the trunk coiling inside the pot. It does a 180 degree sharp turn before coiling back around. Once I sow my acorns, I am cutting them suckers as soon as I can.This one has a halfway decent start to its nebari. I would try cutting it just below the point where several roots flare out at the same level, leaving those finer roots intact.
Bottom of the tree after flattening out the cut.