The Buddha is traditionally said to have attained enlightenment while sitting and meditating underneath the bo tree, or bodhi tree.
The term bodhi is one word for enlightenment, and does not mean a specific type of tree: however, the bodhi tree itself is traditionally understood to have been a ficus religiosa or "sacred fig," also known as a pipal (in Hindi) and an ashwanth (in Sanskrit). Buddhist monasteries in parts of the world in which this tree can prosper will almost invariably have one as one of their most sacred treasures.
Additionally, in order to be designated a bodhi tree today, a tree is supposed to be descended from that original tree by direct propagation from it or one of its descendants. There are several such bodhi trees said to be descended in a direct line from the original bodhi tree under which the Buddha achieved enlightenment; one of those is pictured above.
The sacred fig or ashwanth has a distinctive heart-shaped leaf, clearly visible in the statue of the Buddha under the tree shown below (from the first century AD):
The shape of this leaf is so deeply associated with the achievement of this blessed state, and so imbued with meaning in Buddhist culture that this shape appears in stylized form even with no additional "explanation" necessary:
Now, what I find extraordinarily interesting and significant is the fact that the ashwanth or sacred fig, the very tree associated with the bodhi tree under which the Buddha achieves enlightenment, is associated in the ancient Vedic tradition of India with a specific celestial pair of stars, designated together by the name Pushya.
You can see this ancient association between certain important Nakshatras (stars) and specific tree species attested to in various texts, for example in the scholarly publication of the Proceedings of the Seventh International Congress of Ethnobiology for 2002, and particularly on page 90 of that collection, shown here.
Now, you might be asking yourself which specific star or stars are associated with the Nakshatra known as Pushya! Self . . .
Astonishingly enough, Pushya is associated with two stars: the Northern and Southern Colts, Asellus Borealis and Asellus Australis, which flank the beautiful Beehive Cluster in the zodiac constellation of Cancer, and which we have already seen to have been associated with the Manger in which the Christ is born and the Triumphal Entry into Jerusalem in the New Testament scriptures.
We have also seen that the zodiac sign of Cancer the Crab is located at the very "top of the year" on the zodiac wheel, beginning immediately following the point of summer solstice, and that it is thus associated with the upraised Djed column and all that that powerful symbol was intended to convey, including the "raising up" of the invisible and divine spirit within the individual and within all of the material-spiritual cosmos through which we sojourn in this incarnate life.
Due to this positioning at the "top of the cycle" which the great zodiac wheel symbolizes in its entirety, the upraised arms of the Crab (visible in the constellation itself) were associated in ancient symbolic art and in ancient myth with the upraised arms of the sacred Scarab, with the upraised arms of the ancient Egyptian god of the air (Shu), with theupraised arms of Moses when signaling victory, and with the upraised arms depicted on the sacred Ankh above the vertical Djed column, such as in one famous image from the Book of the Going Forth by Day (also more commonly known as the Egyptian Book of the Dead, or in previous centuries sometimes referred to simply as the Ritual) found in the Papyrus of Ani.
Now, the association of the bodhi tree of the Buddha with the stars of the zodiac sign of Cancer the Crab thus becomes incredibly important, and powerfully resonant with all the other manifestations of this same concept in the ancient wisdom of the world -- the concept which I usually refer to as the "raising of the Djed" with all of its myriad layers of significance.
This association means that, in addition to all else that this "vertical element" in the great cross of the year represents (all that is "vertical" or spirit-elevating in our individual journey and all that brings forth the invisible spirit world that infuses and animates everything in the universe around us), it is also directly related to the concept of enlightenment, of transcendence of the "cast down" condition we experience when we enter into incarnate form and of profound connection with the infinite.
The bodhi tree can thus also be seen to have connections to the World Tree which Odin ascends and upon which he must hang until he is suddenly granted a vision into the invisible realm of the infinite, and to the tree which the shaman ascends literally in cultures around the world as part of the ecstatic journey.
Ultimately, this is a journey undertaken not just by Odin or the Buddha but in fact by every single human soul. I believe (and have quoted Alvin Boyd Kuhn on this specific point several times in the past) no ancient myth or cycle "is apprehended in its full force and applicability until every reader discerns himself or herself to be the central figure in it!"
One need not journey to a specific location where an external Buddha is said to have achieved his enlightenment, nor visit a specific tree reputed to be descended from the very tree under which he sat when he achieved this union with the infinite (although there is nothing wrong with doing so, and it would indeed be a beautiful experience to be in the presence of one of the sacred ficus trees revered and lovingly tended by so many generations of fellow-journeyers through this vale of tears). The bodhi tree, and enlightenment, are in fact inside us at all times (see the tremendously helpful perspective shed upon this concept by Peter Kingsley, discussed here).
We can each sit under that very tree at any time, no matter where in the universe we happen to be.
(Note the two "small celestials" to either side of the Buddha, each of which I have indicated by a red arrow. I believe the Buddha and the bodhi tree in this image clearly relate to the "vertical line" running up from the winter solstice through the summer solstice, while the two flanking figures represent the two equinoxes and the horizontal line between them: the line of being "cast down" into incarnation, which the Buddha and the enlightenment under the fig tree overcome with the "raising back up" of the Djed. In this interpretation, the two flanking figures thus play the same role that Isis and Nephthys play in the Papyrus of Ani image linked before, while the Buddha and the Tree play the same role as the Djed column and the Ankh with upraised arms in that Papyrus of Ani image. This role is also played by Cautes and Cautopates in the Mithraic symbology discussed here).