The World Tree Cosmology

The World Tree cosmology model was outlined in the Year of Wild Magic, 1372 DR, and quickly became the most widely accepted model during those tumultuous times, supplanting the Great Wheel cosmology. The name came from the discovery of a sentient being that manifested itself as a brobdingnagian tree that connected various planes of existence, much like the river Styx. The World Tree cosmological model was invalidated by the Spellplague in 1385 DR and the decade that followed, during which the Elemental Planes collapsed into the Elemental Chaos, the Ethereal Plane and World Tree were destroyed, and the Outer Planes that survived became drifting dominions in the Astral Sea as described by the World Tree model's successor, the World Axis cosmology model.
By the late years of the 15th century DR, some sages began to use again the World Tree cosmology model, despite the fact that other sages preferred to use the Great Wheel or the World Axis models.