':type price: Price
:type price_level: PriceLevel'

def insert(self, price, price_level):

    assert isinstance(price, Price), type(price)
    assert isinstance(price_level, PriceLevel), type(price_level)
    self._price_list.append(price)
    self._price_list.sort()
    self._price_level_dictionary[price] = price_level
