docs: public int find() {
          for (int node = root; node != NIL; ) {
              final int cmp = compare(node);
              if (cmp < 0) {
                  node = left(node);
              } else if (cmp > 0) {
                  node = right(node);
              } else {
                  return node;
              }
          }
          return NIL;
      }