The Romans were not tied to one form of crucifixion. We know this from historical evidence. One example is Seneca the Younger who recounts, "I see crosses there, not just of one kind but made in many different ways: some have their victims with head down to the ground; some impale their private parts; others stretch out their arms on the gibbet.” The available attestation of patristic writers is in agreement with the cross shape.
The Greek word xulon refers to something that is made of wood and can alternatively refer to a tree. The quotation from Deuteronomy (speaking of Galatians 3:13 where the Apostle Paul quotes Deuteronomy 21:22-23) is not referring to crucifixion in its original context. It is referring to the fact that some people were hung on trees in order to communicate that they were cursed by God. Jesus Christ being hung in the air communicated that He was cursed by God for us. This leaves the question as to the shape of the wood that Christ was crucified on. It technically does not matter because He bore our sins anyway. On the other hand, it would be interesting to know. The t shape was the normal form so it would be reasonable to say that He was not crucified on a stake.
Moreover, the biblical evidence that Jesus was nailed to a cross of the traditional shape is strong. Consider the encounter of the doubting Thomas with the resurrected Christ (John 20:24-29). The passage mentions having nails pierced through both hands. That reference to nails is plural. A stake would require one nail. The Scripture records Pontius Pilate nailing an inscription above His head (Matthew 27:37; Luke 23:38). Also, the Apostle Peter was told that he would eventually be made to stretch out his hands for crucifixion by Roman guards (John 21:18). That was the exact posture in which Jesus Himself was crucified previously. So the Jehovah's Witnesses are proven wrong when they insist that Jesus Christ was crucified on a stake. Ironically, the Watchtower Society originally taught that Jesus died on a cross. So much for the claim of being a divinely inspired prophet of God!
The Jehovah's Witnesses deny that Christ resurrected in a glorified physical body. Rather, it is believed that He manifested Himself as a spirit. But Scripture clearly indicates that He was raised from the dead in a physical body (Luke 24:39). He even ate so as to demonstrate to the disciples that He was not a spirit (Luke 24:40-43). The very body of Christ was raised from the dead (John 2:19-22). He was born of a virgin, and so has a body which is permanent. He is both fully human and divine. He is God incarnate. He has been resurrected and glorified for eternity. The denial of a physical resurrection is a pernicious error of the Jehovah's Witnesses.