Unfortunately the picture that comes up on my screen when I click on the link isn't large enough to show the leaves, buds, bark, or fruit size and shape. Are you able to load another picture or resize this one. Might I also suggest adding a familiar sized object like a coke can, quarter, or ruler in the photo for a sense of size and scale. -G

If its a fruiting tree like what I'm familiar (I too am unable to discern much from the small pic) office fluorescents are just not going to do the job. Neither will the (for the most part) stagnant dry air.

It could be that this is some sort of tropical. I wish the pic showed more detail as to the tree type. Tropicals might do well indoors in that environment. The humidifying gravel tray is a waste of effort on your part though. It probably won't hurt anything, but could make for some ugly slime or salt deposits.