Basic Doubts and Concepts to clear

Hi I have a doubt can someone tell why we are using

  • node.left= TreeNode.parse_tuple(data[0])
    and
    -node.right = TreeNode.parse_tuple(data[2])

why we are doing this as in
when we are doing this without class we are simple calling
node.left=parse_tuple(data[0])

does someone know ?