BG Chap 15 - Description of the material world
Kṛṣṇa describes the material world with the use of a metaphor. The material world made of guṇas is compared to an aśvattha tree (banyan tree) with roots upwards and branches downwards. Upwards, in Satya-loka at the top of the universe lies the root of the tree, in the form of four-headed Brahmā composed of mahat-tattva, which is the first sprout from prakṛti. The branches of the tree spread downwards below Satya-loka in the Svar, Bhuvar and Bhūr planetary systems, in the form of devas, Gandharvas, Kinnaras, asuras, Yakṣas, Rākṣasas, men, animals, birds, insects, fish and trees.
The banyan tree of the material world is upside down—roots up and branches down—because it only reflects reality, the reality of the spiritual world. Just as a reflection rests upon water, this tree rests upon the desire of the living entities. As the branches of a real banyan tree produce offshoots that grow down into roots and further trunks, this reflected tree similarly has endlessly complicated, intertwined trunks, roots and branches. One can picture neither its beginning nor its end. A soul situated within the complexities of this incomprehensible tree remains trapped. All existence beyond the tree is forgotten, and he is fully enamored with the tastes of its fruits and berries.