code: def process_tree_recur(self, file_names, node):
          
          # Process node's children
          for child_node in node.children:
              self.process_tree_recur(file_names, child_node)  # Call children first in case a tiled thumbnail is needed
  
          file_names.extend(node.process_files())
docs: Adds the names of all the files associated with the sub-tree rooted by `node` to `file_names` in post-order.
          :param file_names: A global list containing all file names associated with a tree
          :param node: The root of the current sub-tree being processed
          :return: None.