For centuries, the esoteric teachings which we now know as the Kaballah, remained an entirely oral tradition; being handed down from "mouth to ear". Then in the 12th century, written commentaries started to appear; although none of the first Kaballistic treatises were accompanied by diagrams of the Tree of Life, which is the main symbol of Kabbalism.
We are told that the first image of the Tree to be published for public consumption, was on the "PortaeLucis" (Gates of Light), a Latin translation (1516) of Shaare Orah (Gates of Light) written by Rabbi Joseph Gikatalia (1248-1323) around the year 1290. On the title page, a seated man is shown holding a tree with the ten Sepheroth or spheres. Note the triangular shape formed by the top three, then five spheres of the Tree (below, left), and compare with one of the subsequent images of the Tree that have appeared (below, right). Note as well the pentagon directly below the upper triangle, in the left hand image.
The Tree of Life of the later Kabbalists (above right) is taken from Athanasius Kircher's 'Oedipus Aegyptiacus' (1653). I refer to the one as the "A" shaped Tree, and the other as the "H" shaped one. You will note that the advantage of the H style of the Tree, is that it preserves the notion of the three pillars , often associated with the Tree (and said to support the Temple).
We also see rhombus shapes used in the depiction of the Tree of Life, as with this image (below left) from Albert Pike's "Morals and Dogma" (page 770);
and mirrored in Aleister Crowley's 10 of Wands (above right), from his Tarot deck. [Note that each of the tens in Crowley's Tarot deck feature depictions of the Tree.]
As you can see, not everyone is in agreement about the shape of the Tree; then again, not everyone is militant about the "correct" shape, either. But, as with every other form in the history of Mind, in time, there arises a fundamentalist movement or individual proclaiming to posses the Truth about the subject at hand. Such is the case with those who propose that they hold the "proper method of finding the correct centers of the Ten Sephiroth". [On this page, the author asks why there can't be 19 spheres on the tree. They have apparently missed something in their reading.]
Some recommend that the true proportions of the Tree, are to be derived from a model based on the well known Vesica Pisces, where the center of each circle touches the circumference of the ones next to it. Each of the Sephera is located either at the center of a circle (middle pillar) or at the intersection of two circles (the side pillars). [It is presumed that this diagram could be extended ad infinitum.]
Looking at Metatron's Cube, we see that neither the A and H shaped Trees fits the original thirteen circle version of the Cube. The H-shaped Tree (left) requires the use of two of the spheres (for 2 and 3) that were added last, and the A-shaped tree centers these two on the triangle figure in the cube.
In all fairness, it must be pointed out that the H tree looks like a ladder, while the A tree, really does look like a tree; a Christmas Tree in particular.
From: "A NEW ENCYCLOPEDIA of Freemasonry", by A E Waite (p 409)
"Symbolists have the logic of their own images, therefore if their selected type is a tree, then they are not likely to alternatively call it a ladder.
Although the Zohar does depict the "just man" as being a Ladder leading from earth to heaven, with his feet on the earth and his head in heaven, nowhere in the Zohar or the Sepher Yetzirah, the oldest text on kabbalism, are the ten Sephiroth which constitute the Tree of Life compared to the Ladder of Jacob's story.
The conventional diagram now called the Tree of Life, is a device of post-Zoharic Kabalism. The Sephiroth have always represented the scale of ten; we do not know how they were laid out in the Minds of early kabalists, but it certainly was not a ladder."
The Tree of Life, as described by the Hebrew Kabbalists, contains ten sephiroth, or emanations. Synthesized in each sephiroth of the Tree of Life are the concepts, ideas, and attributes that should be meditated on in order to grasp intuitive insights about the Tree. Self-realization occurs when the initiate realizes all ten sephiroth within himself or herself. The Tree of Life is Jacob's Ladder, the Ladder we must climb to reach self-realization, the Ladder of the vertical path.
This figure (indicating an image of the H-shaped Tree) is traditionally called "Jacob's Ladder," indicating that it portrays the esoteric reality behind the Bible story in which Jacob saw a ladder reaching up into heaven, with angels ascending and descending upon it.
More links to sites where the Tree is depicted in some form as Jacob's Ladder.
* While it may be true, that the plot of both the Tree of Life and the Jacob's Ladder stories is concerned with an Exile and a Return, Waite is right, a Tree is not a Ladder.