Not really. Nailing people to a post or tree is crucifixion. Sure it is. Remember the passage, cursed is anyone hung on a tree, applied to Jesus? http://bible.cc/galatians/3-13.htm
Sometimes the Greek word for wood is used of the cross. The word ξύλον "wood" occurs a total of 20 times in the New Testament.
Jesus was crucified on a post with a cross bar as we know to die for our sins. He was cursed on our behalf.
But, I think that nailing someone to a literal tree would still qualify as an act of crucifixion.
This from Wikipedia:
Ancient Greek has two verbs for crucify: ana-stauro (ἀνασταυρόω), from stauros, "stake", and apo-tumpanizo (ἀποτυμπανίζω) "crucify on a plank." [4] together with anaskolopizo (ἀνασκολοπίζω "impale"). In earlier pre-Roman Greek texts anastauro usually means "impale."[5][6][7] The word xylon "piece of wood" was also used, but for a gallows, not a stake, as in the Aristophanes comedy The Frogs; "if you stumble, at least you'll hang from a respectable tree."[8]
The Latin term crux may mean a gallows[9][10] or a stake.[11]
The English term crucifix derives from the Latin crucifixus or cruci fixus, past participle passive of crucifigere or cruci figere, meaning "to crucify" or "to fix to a cross".[12]
(fyi, he was being sarcastic...see the end of his post)
ohutos en telehoroon ouk egenominos ouk aan (apologies for lack of Greek fonts).