I want to build a world tree, literally.
The realm of the dead would be in the roots, the realm of the gods at the treetop.
Each leaf would hold at least a small town (let's say 15km²) and at best a big country (700 000km²). They would mostly have arable land on them for humans to live and prosper. The first habitable leaves would be way above ground so no human could imagine there is one. The biome would vary from leaf to leaf. The branches and the trunk would be arid highways between leaves.
The problem is: I'm having a hard time sizing it all. (I'm mostly asking about lengths.)
How tall would the tree be? How wide? How big would be the trunk? How many leaves will it have?
You can assume any species of tree, even a fantasy one. It only needs to have realistic proportions.