''

def lookup(self, data, parent=None):

    if (data < self.data):
        if (self.left is None):
            return (None, None)
        return self.left.lookup(data, self)
    elif (data > self.data):
        if (self.right is None):
            return (None, None)
        return self.right.lookup(data, self)
    else:
        return (self, parent)
