pub fn root_hash(&self, version: u64) -> anyhow::Result<Option<H256>> {
        let Some(root) = self.db.try_root(version)? else {
            return Ok(None);
        };
        Ok(Some(root.hash::<P>(&self.hasher)))
    }
Returns the root hash of a tree at the specified `version`, or `None` if the version
was not written yet.
core/lib/zk_os_merkle_tree/src/lib.rs