Q.Our Sumac Trunk Split And Keeps Getting Worse I Was Able To Pull It Out Enough To Look Under And See Black
What is it and can it be treated?

Certified GKH Gardening Expert
It looks like wood boring insects have attacked the tree. You can see the entry holes and tunnels. It may be too late to save the tree since there is decay. You may want to contact your local extension agent for more information on local borers and canker. It may have started with a canker disease. Here is more:
https://www.gardeningknowhow.com/ornamental/trees/tgen/tree-borer-insects.htm
https://cisr.ucr.edu/sites/default/files/2019-07/pest_alert_pshb_and_fd.pdf
https://www.gardeningknowhow.com/plant-problems/disease/hypoxylon-canker-fungus.htm