Collected some rocks from around of the same type and different size with one particular decided to cover the front:
Filled in the hole from all sides as tightly as I could without damaging the bark:
Did some grinding of the biggest stone with Dremel like tool so it can fit as close as it could to the front and also fill in the gap inside:
To the stones from the inside I applied epoxy glue being careful not to glue the tree itself:
Pressed well and waited some minutes:
The end result can be seen here.
Perhaps the stone type I used should have been a little bit darker. This one blends with the bark. I thought that would be a good idea but maybe it wasn’t. Anyway, I am OK with the end state, much better than it was anyway 🙂