To be clear, I didn't imply I was agreeing with it. Just saying what the justification for this kind of question is.

I agree completely it eliminates a huge swathe of people, mostly experienced and older people. FAANG employees, ime, are biased towards childless / single people with privileged backgrounds.

Tree inversion sounds weird when you hear it phrased like that, but in an interview it would be explained with an example (just swap the left and right children recursively).