Basic Level categories are instantly recognizable part-whole relationships. They are a "gestalt", where the whole feels more fundamental to us than the sum of the parts.
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One way in which we identify basic-level objects is by **part-whole relationships**. I can tell a tree apart from a bush because trees have a straight up-and-down piece (the trunk) that’s really prominent. It’s notably thicker in relationship to branches than anything a bush has, it’s less obscured by leaves, and so on. Chairs are chairs because they have backs and seats, which are flattish parts at something like a 90 degree angle to each other. Even a bean-bag chair has a seat and a back; it’s irrelevant that those parts are made by someone sitting in the chair and scooching around to shape it, rather than being built that way in the first place.
Tzeltal Speakers» (experts in trees) presumably key in on properties of trees that I don’t see. It could be something like leaf shape, though honestly, looking at pictures of oak leaves and maple leaves, I saw a lot that could belong to either. It could be leaf arrangement: Wikipedia tells me that oak leaves are “spirally arranged” whereas maple leaves have an “opposite leaf arrangement.” I have no idea what that means, but I expect that a tree person can tell the difference from a distance, and at a glance. Indeed, a property of the basic level is that classification is fast. Lakoff says that basic level objects are perceived as Gestalts𓇯,” wholes recognizable without first having to reduce them to their parts.
In his book *Thinking: Fast and Slow 
*, Daniel Kahneman divides mental processing into two… parts… or “systems”: One is fast and automatic; the other is comparatively slow and effortful. Perception of the basic level seems to be fast, suggesting it’s done by System 1, whereas other levels are slower, suggesting System 2.