What does HashNode have a `hash` field?

[GrapeBaBa]

type HashedNode struct {
    hash       *Fr
    commitment *Point
}

In current code base, actually serializing and parsing node are just using commitment, what is the purpose for hash?

[gballet]

Hash is used to cache the serialization when needed. I don't think it's used in too many places anymore, but its presence makes sense because calculating the serialization of a commitment is quite expensive. I expect it will be used again when optimization becomes a topic, assuming we keep the same serialization algorithm.