fn push_level_from_db<'a>(&mut self, level: impl Iterator<Item = (&'a NodeKey, Node)>) {
        let level = level
            .map(|(key, node)| {
                let node = WorkingNode::new(node, Some(key.version));
                (*key.nibbles.bytes(), node)
            })
            .collect();
        self.changes_by_nibble_count.push(level);
    }
The pushed nodes are not marked as changed, so this method should only be used
if the nodes are loaded from DB.
core/lib/merkle_tree/src/storage/patch.rs