Solution to programming challenge (print binary tree elements in order) from https://www.youtube.com/watch?v=OTfp2_SwxHk

btree.py

class BinaryTree:
    left = None
    right = None
    value = None

    def __init__(self, *initial):
        self.value = initial.pop(0)
        for i in initial:
            self.add(i)

    def add(self, new_value):
        if new_value > self.value:
            if self.right is None:
                self.right = BinaryTree(new_value)
            else:
                self.right.add(new_value)
        elif new_value < self.value:
            if self.left is None:
                self.left = BinaryTree(new_value)
            else:
                self.left.add(new_value)
    
    def ordered_print(self):
        if self.left is not None:
            self.left.ordered_print()

        print(self.value)

        if self.right is not None:
            self.right.ordered_print()

    def ordered_list(self):
        lst = []
        if self.left is not None:
            lst += self.left.ordered_list()

        lst.append(self.value)

        if self.right is not None:
            lst += self.right.ordered_list()

        return lst

#     1
#    / \
#   0   2
#      / \
#   None  3
root_node = BinaryTree(1, 2, 3, 0)

print(root_node.ordered_list())

Astute readers will notice we (fati and me did this because we couldn't sleep last night) didn't do the second part, which is printing them in order iteratively, without recursion.