On that same kind of line of thought, the brain and the nervous system (they knew back in the late 1800s or early 1900s that nerve matter was in ALL CELLS of the body). The nervous system is like a branches of roots reaching out as part of facilitating the Earth Experience. The tree although if turned upside down becomes more apparent--or perhaps its more like weeping willow style system where the leaves and branches flow downwards (into the body).
Attachment 3048
The nerve fibres of a live brain were traced by diffusion spectrum imaging, and coloured to represent their direction.
In a traditional sense, the nervous system extensions below the base of the skull might correlate to the roots of the tree that are underground. The brain itself might best correlate to leaves and systems above ground (kind've like a bush). No doubt, you could see how the body could be a type of sensory deprivation chamber or 'focus chamber' for multi-dimensional beings.