Looking at the 13th century painting of the Crucifixion on the right, a Forked Cross would probably have been difficult and costly to construct, and it's unlikely that such a cross was made for Jesus' Crucifixion. However, the Bible1 does say that Jesus was crucified on a tree, and it is from there we get this 'Y' shape.
Another name given to this cross is the Thief's Cross or Robber's Cross, since it is believed that criminals in Roman Judea were crucified on a forked cross. However, like many symbols described on this site, there is little irrefutable evidence about their origins.
Examples can be seen in church logos, such as those of the Anglican Church of Kenya (ACK) www.ackenya.org/ and the Anglican Church of Tanzania (ACT) www.anglican.or.tz/
Most paintings of Jesus on this shape of cross tend to be from the medieval period and show a corpus attached. Some people see the 'Y' as the initial letter of Yahweh (God's name in Hebrew).
With its three members, the Forked Cross reminds us of the Holy Trinity and it is often seen on clerical vestments, such as the chasuble (a sort of poncho worn by Lutheran, Anglican and Catholic priests during Mass). And this leads us to alternative terms - Yoke Cross, Vestment Cross or Pall Cross; pall being an old name for a robe or cloak. However, pall is also a generic name for a cloth that is draped over many different things - a coffin, a corpse, or an altar for example. When a cross is stitched onto a pall, that cross has perhaps more right to be called a Pall Cross.
Moving away from Christianity and a few hundred years before Christ, Pythagoras added the letter upsilon to the Greek alphabet, which is '' in uppercase and 'u' in lowercase. Pythagoreans are said to view the 'Y' as a symbol of one's journey through life. We start life at the bottom of the Ypsilon Cross (Y-shaped Cross) and work our way up through adolescence to the intersecting point. Here, at the crossroads of life, we cannot go forward but must choose whether to branch right, the difficult road following the goddess of Aretê (Virtue) for a blessed life, or branch left on the easy path following the goddess Kakia (Vice) to a life of ruin.
Matt. 7:13-14 tells us to "Enter through the narrow gate. For wide is the gate and broad is the road that leads to destruction, and many enter through it. But small is the gate and narrow the road that leads to life, and only a few find it."
Is it coincidence that the Roman font for the letter 'Y' has a broad left arm and a narrow right arm, symbolizing the wide and narrow roads?
Is it coincidence that Microsoft's webdings font displays a love heart symbol for the uppercase letter 'Y'?
Another cross has forks at the end of each arm, called a Moline Cross (Millrine, Millrind, Fourche, Anillée, Nillée, Anchory Cross or Ancrée).
Another name for these multiple-forked crosses is Furca, and that name was also used for an A-frame (inverted Y-frame) used to punish slaves and criminals. Like a yoke, the heavy wooden frame was placed on the victim's shoulders and his hands were tied to the bottom ends. They then had to carry this burden for the duration of their punishment to hinder further crime. Sleeping, eating, using the toilet; all would be a challenge. When they were released, there would be much work to catch up on. The device could easily be used for crucifixions.