Terumot and ma'aserot from produce belonging to a non-Jew

Question

Produce that was grown by an Arab and harvested by an Arab is not obligated in terumot and ma'aserot. The final "processing" - gemar melachah - needs to be performed by a Jew to be obligated in terumot and ma'aserot, even if the produce belonged to a non-Jew. Given that it's his tree and he harvested it and brought it to the office, you do not need to separate terumot and ma'aserot.