For Buryatian Bo Morgul, the cosmos, Zambi Tubi, is an immeasurable sphere represented by a circle which contains the Three Worlds (the Upper World, the Middle World and the Underworld) stacked on top of the other. Eah of these three worlds encompasses the four directions: Front (south), Behind (north), Right (west) and Left (east). All the realms are held together either by means of the Cosmic Mountain, or Sumber or by the Sacred Tree Serge which serves as the axis mundi and penetrates all three worlds from the bottom to the top.
Dmitry Ermakov in Bo & Bön p. 144