A minimal Python implementation for binary trees

trees.py

# University of Bologna
# First cycle degree in Mathematics
# 07276 - Computer Science
#
# Stefano Volpe #969766
# 06/18/2021
#
# trees.py: tree class implementation

class tree:
    def __init__(self, label=None, sx=None, dx=None):
        self.__label = label
        self.__sx = sx
        self.__dx = dx
        if label is not None:
            if sx is None:
                self.__sx = tree()
                self.__dx = tree()
    def label(self):
        return self.__label
    def first_child(self):
        return self.__sx
    def second_child(self):
        return self.__dx
    def is_empty(self):
        return self.__label is None
    def is_leaf(self):
        return not self.is_empty() and self.__sx.is_empty() \
        and self.__dx.is_empty()
    # def __str__(self): # The default implementation calls object.__repr__()
    def __repr__(self):
        res = "tree("
        if not self.is_empty():
            res += self.label().__repr__()
            if not self.is_leaf():
                res += ", " + self.first_child().__repr__() + ", " \
                + self.second_child().__repr__()
        return res + ")"