Question on Skill Path - Choose 1 of 3 - But Also Have 1 From Unique? So 2?

For Ice Shard I chose Glacial Spike as the 1 of 3 I can choose. It says we can only have one. Ok that makes sense. But I picked up a unique for Ice Shard that has the Piercing Cold upgrade which is pretty nice. Will that work with the chosen skill from the skill tree or will it be negated since I can only "choose" one from the tree. Not sure if that means also if I can only have one active if i found one in an armor buff - Hail of Verglas