Function root_from_proof 

pub fn root_from_proof(
    leaf: Digest,
    index: usize,
    proof: &[Digest; 7],
) -> Option<Digest>

Recover a root from a public-key commitment and checked leaf index.

Bit level of index says whether the running hash is a left (0) or right (1) child at that level. Returns None for an index of 128 or more.