does anybody know how many leaves trees are supposed to have?

I hope this isn't a troll question, but serious curiosity. There is no specific
number. It depends on species, location, and many other factors. The larger the
tree, the more leaves it will have. Generally, a tree with large leaves, like a
sycamore, will have fewer of them. The same species in shade will have fewer &
larger leaves than in sun.
At one extreme, Welwitschia mirabilis, a primitive conifer from Africa, has
only two leaves its entire life, which may be 2000 years. The same two leaves
keep growing from the base as they wear out on the end. At the other extreme,
there are trees that grow in the desert or the far north, both conifers and
flowering trees, like Junipers and Tamarisks, which have thousands of tiny
scale leaves or needles you couldn't begin to count. If a tree is healthy and
growing, you can assume it has as many leaves as it should.
Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)