Kether, the Sephirah at the apex of the Tree of Life, is the seed source of all things that participate in the Divine Life. It is represented by a point. The horizontal path with Chokmah and Binah at its ends constitutes a straight line. Chesed, Geburah & Tiphareth are at the vertices of a triangle. Netzach, Hod, Yesod & Malkuth are at the vertices of a tetrahedron. The point, line, triangle and tetrahedron constitute the 'trunk' of the Tree of Life. The remainder of the Tree of Life, represented by the dotted lines and the triangles that they form, constitutes its 'branches'. The trunk is therefore the essential, geometric representation of the integers 1, 2, 3 & 4, symbolized by the four rows of yods in the tetractys.