That looks to be an old wound attempting to heal. It's hard to say from what . Does it face west??? Possibly frost crack/sunscald???
The tissue needs to "roll over" and close in. Keep the wound clean of debris and carve a smooth surface for the tissue to adhere to as it slowly begins to seal. Watch that a pocket does not form at the base. This will give an easy place for decay/rot to form. Bark tracing is another step in the repair but from what I see (and I can't see the bottom) it doesn't need it.
Certified Kansas Arborist since 1982