Binary Tree and Pre-In-Post order Iteration | Python 3.8

# Python 3.8
"""
Task: build a Binary Tree from a given array of integer in Python.
Use the Pre, In, and Post Order iteration to print the values.

Example of tree:
     0
   1   2
  3 4 5 6
"""

# • functions and classes start here •
class Node:
    value = 0
    left = None
    right = None

# tree building function
def buildTree(a, indx):
    if indx < len(a):
        root = Node()
        root.value = a[indx]
        root.left = buildTree(a, 2*indx+1)
        root.right = buildTree(a, 2*indx+2)
        return root
    else:
        return None

# pre-order function
def preOrder(root):
    print(root.value)

    if root.left != None:
        preOrder(root.left)

    if root.right != None:
        preOrder(root.right)

# in-order function
def inOrder(root):
    if root.left != None:
        inOrder(root.left)

    print(root.value)

    if root.right != None:
        inOrder(root.right)

# post function
def postOrder(root):
    if root.left != None:
        postOrder(root.left)

    if root.right != None:
        postOrder(root.right)

    print(root.value)

# • main starts from here •
#array = raw_input().split()
a = [0, 1, 2, 3, 4, 5, 6] # test array
root = buildTree(a, 0)

print("pre order:")
preOrder(root) # output: 0, 1, 3, 4, 2, 5, 6

print("\nin order:")
inOrder(root) # output: 3, 1, 4, 0, 5, 2, 6

print("\npost order:")
postOrder(root) # output: 3, 4, 1, 5, 6, 2, 0