binary_tree.py

class BinaryNode:
    def __init__(self, value):
        self.value = value
        self.left = None
        self.right = None
    
class CompleteBinaryTree:
    def __init__(self, start: BinaryNode) -> None:
        self.start = start
        self.counter = 0
    
    def insert(self, new: BinaryNode) -> None:
        def recursion(new: BinaryNode, layer: [BinaryNode]):
            nextLayer = []
            for node in layer:
                if node.left == None:
                    node.left = new
                    return
                else:
                    nextLayer.append(node.left)
                if node.right == None:
                    node.right = new
                    return
                else:
                    nextLayer.append(node.right)
            return recursion(new, nextLayer)

        recursion(new, [self.start])

binary_tree_test.py

import unittest
from binary_tree import BinaryNode, CompleteBinaryTree

def init_complete_tree():
    n1 = BinaryNode(1)
    n2 = BinaryNode(2)
    n3 = BinaryNode(3)
    n1.left = n2
    n1.right = n3
    return CompleteBinaryTree(n1)

class BinaryTreeTest(unittest.TestCase):

    def test_insert_complete(self):
        tree = init_complete_tree()
        n4 = BinaryNode(4)
        n5 = BinaryNode(5)
        n6 = BinaryNode(6)

        tree.insert(n4)
        tree.insert(n5)
        tree.insert(n6)

        n2 = tree.start.left
        n3 = tree.start.right

        self.assertEqual(n4, n2.left)
        self.assertEqual(n5, n2.right)
        self.assertEqual(n6, n3.left)