@nprofile1q... yeah Tree is really in need of optimization. My approach is to load stuff on demand.
But even still, 5.5GB for only 73500 entries is too much. Perhaps you're doing something else when you populate the Tree that makes it jump this much?
My Tree with 148K entries makes my RAM jump from 124.2MiB to 1.67GiB once I expand all (and load all entries).