When I first starting observing for iNat, I confused Trembling Aspen trees for Birch.
https://www.inaturalist.org/observations/38061026
https://www.inaturalist.org/observations/39063233
The tops looked like Birch to me but the bottoms are darker. It was one of the first things I ‘learned’ (by making a mistake in id) at iNat!