All the previous Tree BFS Level Order Examples are returning something, why aren't we doing it here? Is it inherent that the tree is being returned?

Also why does this one include the print function but previous versions don't? This makes it so you don't see the input and output when the Solution is Executed.

from __future__ import print_function
from collections import deque


class TreeNode:
  def __init__(self, val):
    self.val = val
    self.left, self.right, self.next = None, None, None

  # level order traversal using 'next' pointer
  def print_level_order(self):
    nextLevelRoot = self
    while nextLevelRoot:
      current = nextLevelRoot
      nextLevelRoot = None
      while current:
        print(str(current.val) + " ", end='')
        if not nextLevelRoot:
          if current.left:
            nextLevelRoot = current.left
          elif current.right:
            nextLevelRoot = current.right
        current = current.next
      print()


def connect_level_order_siblings(root):
  if root is None:
    return

  queue = deque()
  queue.append(root)
  while queue:
    previousNode = None
    levelSize = len(queue)
    # connect all nodes of this level
    for _ in range(levelSize):
      currentNode = queue.popleft()
      if previousNode:
        previousNode.next = currentNode
      previousNode = currentNode

      # insert the children of current node in the queue
      if currentNode.left:
        queue.append(currentNode.left)
      if currentNode.right:
        queue.append(currentNode.right)


def main():
  root = TreeNode(12)
  root.left = TreeNode(7)
  root.right = TreeNode(1)
  root.left.left = TreeNode(9)
  root.right.left = TreeNode(10)
  root.right.right = TreeNode(5)
  connect_level_order_siblings(root)

  print("Level order traversal using 'next' pointer: ")
  root.print_level_order()


main()