docs: def get_combo(self, symbol):
          """ get group by child symbol """
          for parent, legs in self.instrument_combos.items():
              if symbol == parent or symbol in legs.keys():
                  return {
                      "parent": self.get_instrument(parent),
                      "legs": legs,
                  }
          return {
              "parent": None,
              "legs": {},
          }