It derives from the verb “trepar”, which means “to climb” (esp. to climb without external aids likes ropes and such – that is, to climb something using only your hands, feet and perhaps teeth ).
A “trepa” is someone who will climb higher (at work, or in the social ladder), NO MATTER WHAT. A “trepa” will only think about him- or herself, will ruthlessly squash others under his or her feet to go up, and will use others left and right to achieve whatever manoeuvres allow for a speedier climb towards the top. And damn the consequences!
I don’t know if this would cover the kind of person the OT had in mind…