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I suspect that the damage was caused by beetles in the order Coleoptera, most likely from the families Cerambycidae or Buprestidae. The affected material was found on sessile oak (Quercus petraea), and the tree was already dead.
Answer
Dear Karlo. The gallery belongs to Cerambycidae family and it is most probably the genus Plagionotus. On oaks there develops many Cerambycid species so it is hard to say witch one is it without imago picture. All the best, Juraj.