To distinguish from actual trees.

Hmmmm, it is pretty interesting question. I think the reason why we draw them upside down is the fact that we have not seen real trees.

What do you mean by upsite down? Don't trees look like that irl too?

Cause we programmers know our responsibility towards the environment and we don't cut real trees recklessly just for our selfish motive of solving problems. Hence we only use artificial trees that differ significantly from real trees.

In order to draw them starting from leaves, you would need to compute all depths first to know where to draw each vertex.

Same reason (in most cultures) we write top to bottom

I couldn't understand what you're talking about. Doesn't this look realistic?

May be programmers visualize the roots instead of the brunches of a tree.

False. They are not upside down. Real trees are the ones which are upside down.

i was about to ask the same question, why are trees upside down irl

we write and read things top-bottom, i think i feels natural and easy to do same with trees

.