I don't think any one type is over- or underrepresented as a whole, but if you're used to playing competitive singles a lot of Stealth Rock weak Pokemon don't register as much of a threat to you. Moltres and Volcarona are other good examples of this. Ice types definitely have a lot of inherent volatility with Snow Cloak, freezing, and Sheer Cold, which probably make them unusually memorable. Nothing's immune to them so you can't really play the switch-stalling game unless you have Chansey or a super bulky Water type with Scald.Is it just me, or are Ice types unusually common in the Battle Tree? I nearly lost my Doubles streak to a team of Alolan Ninetales, Mamoswine, Glaceon, and Moody Glalie. No, it wasn't the Moody that gave me problems.
(Trivia Time: Moody is called "Veleta" in Spanish, which means "weathervane".)