"Not one tree stands next to the city, but two."
Translation:A város mellett nem egy fa áll, hanem kettő.
I believe we always put a comma before hanem and other contrasting words in Hungarian, so that's the rule.
Should there be another comma here after kettő: Nem egy fa, hanem kettő áll a város mellett.
Oh dear, higher spheres of foreign languages. :´)
My feeling says that there's no need to put a comma there, since kettő is still part of the subject of the main clause.