#### Inorder Tree Traversal 2022

p
```"""
Illustrate how to implement inorder traversal in binary search tree.
Author: Gurneet Singh
https://www.geeksforgeeks.org/tree-traversals-inorder-preorder-and-postorder/
"""

class BinaryTreeNode:
"""Defining the structure of BinaryTreeNode"""

def __init__(self, data: int) -> None:
self.data = data
self.left_child: BinaryTreeNode | None = None
self.right_child: BinaryTreeNode | None = None

def insert(node: BinaryTreeNode | None, new_value: int) -> BinaryTreeNode | None:
"""
If the binary search tree is empty, make a new node and declare it as root.
>>> node_a = BinaryTreeNode(12345)
>>> node_b = insert(node_a, 67890)
>>> node_a.left_child == node_b.left_child
True
>>> node_a.right_child == node_b.right_child
True
>>> node_a.data == node_b.data
True
"""
if node is None:
node = BinaryTreeNode(new_value)
return node

# binary search tree is not empty,
# so we will insert it into the tree
# if new_value is less than value of data in node,
#  add it to left subtree and proceed recursively
if new_value < node.data:
node.left_child = insert(node.left_child, new_value)
else:
# if new_value is greater than value of data in node,
#  add it to right subtree and proceed recursively
node.right_child = insert(node.right_child, new_value)
return node

def inorder(node: None | BinaryTreeNode) -> list[int]:  # if node is None,return
"""
>>> inorder(make_tree())
[6, 10, 14, 15, 20, 25, 60]
"""
if node:
inorder_array = inorder(node.left_child)
inorder_array = [*inorder_array, node.data]
inorder_array = inorder_array + inorder(node.right_child)
else:
inorder_array = []
return inorder_array

def make_tree() -> BinaryTreeNode | None:
root = insert(None, 15)
insert(root, 10)
insert(root, 25)
insert(root, 6)
insert(root, 14)
insert(root, 20)
insert(root, 60)
return root

def main() -> None:
# main function
root = make_tree()
print("Printing values of binary search tree in Inorder Traversal.")
inorder(root)

if __name__ == "__main__":
import doctest

doctest.testmod()
main()
```