In 2e Trees of life were created by wizards to combat the destruction of nature (Original Rules Book, pg 62).
They could be created by a 6th level Sphere of the Cosmos spell and an 8th level Wizard spell. (Confirmed in Dragon Kings as 6th Sphere of Cosmos and 8th level Wizard spell)
The revised boxed set continued with it being 6th Cosmos/8th Wizard and confirmed it’s origin (pg 79) but changed it to a 7th level Wizard spell in Defilers & Preservers pg 26 - probably an error.
3e changed it to non-defilers can create. I covered a bit of it in the link below, but that thread has more details on Trees of Life.