The Basic Level𓇯 of categorization doesn't depend so much on the structure in the world as on our experience of it. Someone who doesn't interact much with trees might call a White Oak "a tree" when asked "What's that?" Someone to whom trees *matter* might say "an oak" (but probably not "a White Oak").
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As a suburban boy, “tree” is the basic level word for me. But Tzeltal speakers» were less abstract: they used words like “oak” and “maple”, one level more concrete than “tree”. They did that because trees were more important to them; they attended to them more and so could recognize important distinctions that don’t matter to me.
We can call the basic level the default choice. For example, if it’s autumn and the ground around a tree is littered with acorns, even I will know it’s an oak tree. But I’ll likely still say it’s a “tree.” To me, that’s the word I’d think most useful to a listener.