':param tick: A tick to represent in the order book
:param price_level: A price level to place the tick in
:type tick: Tick
:type price_level: PriceLevel'

def __init__(self, tick, price_level):

    assert isinstance(tick, Tick), type(tick)
    self._tick = tick
    self._price_level = price_level
    self._prev_tick = None
    self._next_tick = None
