Its branches are nourished by the gunas with sense objects as their shoots below and above. And below, the diffused roots are the karmas that bind (one) in the world of mortals.
Krishna compares the whole of samsara to a banyan tree, something similar to the tree of life you saw in the movie Star Wars. It’s a huge tree covering acres of land and all your fears confront you when you enter the domain of the tree. Similarly, here, the whole of samsara, the manifested world which makes you feel finite, with all the different dimensions, is compared to a tree. It’s a huge Ashvatha tree, generally translated as a peepal tree, but the description is closer to that of a banyan tree. As a banyan tree has a trunk and the roots too are above, people misinterpret this to be an upside down tree. What is meant here is that the root of this tree or the source of this tree is in Brahman and Brahman is beyond or above your experience. As Brahman is beyond your experience, it’s pointed out that the root is above, above human experience, but not above human validation or human understanding. And samsara is what you experience and that is

below, meaning it is in our dimension where we can experience it. Krishna continues describing it by saying that all the gunas or vishayas, its branches, are spread both above and below. They spread above into higher dimensions like heaven, etc., and below into the world of men; it is earth and our dimension of life and it is nourished by maya i.e; the gunas which are sattva, rajas and tamas.
The sense objects are the buds which see the world outside and impel men to action, and from action comes karma and from karma comes phala (the fruit or results of action). To experience all the karma phala, you need more janma (births). Therefore, Krishna says, ‘Karmena anubandhi’, you are bound by karma in the world of mortality, because there is no end to it. Once you are in samsara, it keeps going, it is self-perpetuating, because one thinks one is finite and one is not happy with it and so one wants to get rid of the feeling of finitude by doing actions to get things that make one feel fulfilled. Either that or one takes action to get rid of things that make one unhappy and finite. The person thinks that happiness is out there and that pursuing this happiness

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