Hello Linda. I'm not sure what it is you're trying to show us. What should we be looking at?

If, as it looks to be, the oak stump is dead, It starts to decay - as it does, various insects, bacteria and fungi will invade the dead wood. They do this as part of the decay or recycyling process - some insects may make their home in it for a while, till it crumbles altogether. I'm afraid its part of the natural process of life (or death and decay, in this case). Treatment is impossible, and unnecessary - what you're seeing is nature in action.