I will play with winter tree but it is because I adore frost effects. I don't get design choices very often. Why is fire considered more damaging than ice. i would rather get burnt than frostbitten, I would prefer a fire blast in my face than ice spike. Walking through fire wall would be much more pleasant than ramming ice wall. I guess I miss frost spells in form of damage.
Actually, its weird but Fire being the highest damage tree for mages is pretty much the cliche in most games with magic. Its like that in every game. Fire is high damage, ice slows and damages, lightning paralyses...etc...
I guess its because people think of fire and they think agressiveness and destruction? Who knows...
Personally, my favorite trees are Ice and Lightning. Plus the Winter Stillness skill that lets your mana regeneration increase when standing still is like a must for all my mage characters in DAI. Having barrier and the skill in the barrier tree that reduces your aggro is also worth the 2 point investment into the barrier tree.
Of course, its good to have one fire skill, one lightning skill, and one ice skill just to deal with elemental affinities in some monsters. (despair demon, wrath demon...etc)
Finally, Ice Wall is stupid. It could be so useful, but you can't attack over it, so you pretty much lock yourself out of fighting if you place an ice wall before you to protect you. 