This is indicative of an insect borer.  When the tree as cut down, the insect was in the larval or pupal state inside the tree.  The insect pupates and chews its way out to emerge as an adult.  There may be more pupae that have yet to emerge, so I'd recommend storing wood outside away from any structures.  Here is a factsheet for additional reference:  https://entomology.ca.uky.edu/ef210#:~:text=Flat%2Dheaded%20apple%20tree%20borers%20attack%20primarily%20unhealthy%20or%20newly,are%20evidence%20of%20their%20activity.

Best, 

Jen