Jesus was crucified on a cross, not a literal tree that had leaves on it.  The Greek words for cross and tree are different.  Let’s take a look.  The Greek word for cross is σταυρός “stauros”:

“literally cross, an instrument of capital punishment, an upright pointed stake, often with a crossbeam above it, or intersected by a crossbeam (MT 27.32); (2) by metonymy, as the means of atonement punishment of the cross, crucifixion (PH 2.8); as a religious technical term representing the significance of the atoning death of Jesus in the Christian religion cross (1C 1.18); metaphorically, the dedication of life and the self-denial that a believer must be prepared to take on himself in following Christ (LU 14.27)”¹Friberg, T., Friberg, B., & Miller, N. F. (2000). Vol. 4: Analytical lexicon of the Greek New Testament. Baker’s Greek New Testament Library (355). Grand Rapids, Mich.: Baker Books.

The word (σταυρός, stauros) “cross” occurs 27 times in the New Testament in 27 verses: Matthew 10:38; 16:24; 27:32; 27:40; 27:42; Mark 8:34; 15:21; 15:30; Mark 15:32; Luke 9:23; 14:27; 23:26; John 19:17; 19:19; 19:25; 19:31; 1 Cor. 1:17; 1:18; Gal. 5:11; 6:12; 6:14; Eph. 2:16; Phil. 2:8; 3:18; Col. 1:20; 2:14; Heb. 12:2. Never once does the word mean a literal tree growing in the ground. It means cross.

Now, let’s focus on one of them, Matt 27:40 which says, “You who are going to destroy the temple and rebuild it in three days, save Yourself! If You are the Son of God, come down from the cross.”

This is a definitive verse that deals with exactly what Jesus was crucified on, and the Greek word in the verse is “stauros.”  Therefore, Jesus was crucified on a cross, not a tree.

Tree

Tree, as in a growing plant with branches, is the greek word δένδρα “dendra” and it occurs 25 times in 18 verses in the New Testament: Matthew 3:10; 7:17; 7:18; 7:19; 12:33; 13:32; 21:8; Mark 8:24; Luke 3:9; 6:43; 6:44; 13:19; 21:29; Jude 12; Revelation 7:1; 7:3; 8:7; 9:4.

There is no use of the word “tree” (δένδρα “dendra”) in reference to the cross.  If that is so, then why do some Bibles translate it into the word “tree” when referencing Jesus’ crucifixion?  For that, let’s look at a third word.

Wood

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.  Those that refer to the cross of Christ are:

• Acts 10:39, “We are witnesses of all the things He did both in the land of the Jews and in Jerusalem. They also put Him to death by hanging Him on a cross (ξύλον, wood).”
• Acts 5:30, “The God of our fathers raised up Jesus, whom you had put to death by hanging Him on a cross(ξύλον, wood).”
• Acts 13:29, “When they had carried out all that was written concerning Him, they took Him down from the cross (ξύλον, wood) and laid Him in a tomb.”
• Galatians 3:13, “Christ redeemed us from the curse of the Law, having become a curse for us—for it is written, “Cursed is everyone who hangs on a tree (ξύλον, wood).”
• 1 Peter 2:24, “and He Himself bore our sins in His body on the cross (ξύλον, wood), so that we might die to sin and live to righteousness; for by His wounds you were healed.”

So we see that the Bible uses the terms interchangeably.  But this doesn’t mean that Jesus was crucified on a literal tree.  Remember, above in Matt 27:40 we see exactly which word is used to describe what Jesus was crucified on, a cross.

“You who are going to destroy the temple and rebuild it in three days, save Yourself! If You are the Son of God, come down from the cross,” (Matt. 27:40).

Conclusion

Jesus was crucified on a cross, not a tree.