This is a large ichneumon, probably Megarhyssa macrurus, with a very long ovipositor embedded in the trunk of a tree. The stated size does not include the length of the ovipositor. Presumably, there is some kind of larva at the other end of the ovipositor. Actually, there appear to be two separate appendages coming out of the body, but one wraps around the other at the point where they enter the tree. The image has been rotated 90° left for clarity. The insect was actually in a head down position.