15.1 Urdhva-mulam, that which has its roots upwards:- Brahman, possessed of the unmanifest power in the form of Maya, is referred to by the word 'upward' because of Its subtleness in point of time by virtue of Its being the Cause, and also because of Its eternality and vastness; and That is the root (mulam) of this world. The Tree of the World which is such, is urdhva-mulam. This accords with the Upanisadic text, 'This has its roots above and branches below' (Ka. 2.6.1). In the Purana also we have:
It sprouts from the Root in the form of the Unmanifest; it grows through the sturdiness of that very One. And it has abundance of intelligence as its trunk, and the appertures of the organs as the hollows.
The great elements are its boughs [A.G. takes the word visakha (boughs) in the sense of stambha, perhaps meaning the aerial roots.-Tr.]; so also, it has the objects of perception as its leaves. It has virtue and vice as its beautiful flowers, and happiness and sorrow are the fruits it bears.
This eternal Tree presided over by Brahman is a means of livelihood to all creatures. And this verily is the resort of Brahman [Or, etat brahma-vanam means: This Tree has Brahman as its object of adoration, its support. For, the world has nothing but Brahman as its support.] in it Brahman dwells for ever.
Having felled and split this Tree with the great sword of Knowledge, and then attaining the bliss of the Self, one does not return from that (bliss).' (Cf. Mbh. As. 47.12-15.)
That Tree which has its roots upwards and is constituted by the enchantment of mundane existence, and adhah-sakham, which has the branches downwards-mahat, [See under 7.4.-Tr.] egoism, subtle elements, etc. are its branches (sakhah), as it were, extending downwards (adhah); so, it has its branches downwards-; that Tree with its branches downwards, which does not (a) last (stha) even for the morrow (svah), is asvatthah (lit. Peepul tree). Ahuh, they say; that the asvatthah, Peepul Tree, undergoing destruction every moment; is avyayam, imperishable, and constituted by the enchantments of mundane existence. Having been in existence from time without beginning, that Tree of the World is imperishable. It is, indeed, will known as the sustainer of the beginningless and ceaseless series of bodies etc. They call that the imperishable.
Of that very Tree of the World here is another alification: Yasya, that Tree of the World of which; chandamsi-chandas being derived in the sense of covering (protecting)-, the Vedas in the form of Rk, Yajus and Sama; are the parnani, leaves, 
as it were. As leaves serve as protectors of a tree, so the Vedas serve as the protectors of the world; for they reveal what are virtue and vice as also their causes and results.
Yah, he who; veda, knows; tam, that-the Tree of the World along with its root, as has been explained; sah, he; is a vedavit, knower of the Vedas, i.e. versed in the meaning of the Vedas.
Since, apart from this Tree of the World along with its root, not even an iota of any other thing remains to be known, therefore he who knows the purport of the Vedas is omniscient. In this way the Lord euligizes the knowledge of the Tree together with its root.
An imagery of the other parts of that very Tree of the World is being presented: