{"ast_node_type":"other","tokens":[{"end":89,"kind":"keyword","start":0,"text":"parent.push(PreorderIndex::ZERO);"}]}
    parent.push(PreorderIndex::ZERO); // the parent of the root node is the root for now.
    pre_order_to_real.push(graph.start_node());
    real_to_pre_order[graph.start_node()] = Some(PreorderIndex::ZERO);