Building a city inside a giant hollowed-out tree — thoughts?

I'm drafting a druidic city called Glimmerwood built entirely within the trunk and branches of an ancient, miles-wide redwood tree.

How would such a city handle basic logistics like sanitation, water distribution to upper levels, and fire prevention? Let's brainstorm!

For water, perhaps the tree itself has massive internal sap-channels that pump freshwater to the canopy, which the citizens tap into?