Does order_book_path[0] represent the parent node of order_before?

[cryptocj]

In circuit/src/matching_engine.rs, the get_quote function uses order_book_path[0]:

let sibling_ask_base_diff =
    builder.sub(order_book_path[0].ask_base_sum, order_before.ask_base_sum);

Does order_book_path[0] represent the parent node of order_before?

If so, this would mean order_book_path[0] is not the leaf level, but rather the first internal node (level 1) above the leaf.

Thank you!