I have no doubt there will be trees on the big terraces. There won't be any on the individual terraces that stair-step up the building, though.
It's pretty easy to do rooftop vegetation these days. The key thing is that you need to build pits for the trees' root systems, and the bigger the pit, the bigger the tree can grow. The easiest way is to build planter boxes for the trees, which can also provide seating around the edges. This allows the underground pits to be shallower. You can also do fully-sunken pits like at the WTC Memorial, but this requires a ton of space - you might need to consume the floor beneath.
These are hawthorn trees - ugly as hell, but when Dan Kiley gets his hands on them, they turn into sheer magic. I had the privilege of eating lunch here virtually every day last summer. This is built atop the roof of some underground facilities.