code: def get_file_diff(tree, files_to_diff):
      
      # Determine which files have not yet been uploaded to the CC server
      config.LOGGER.info("\nChecking if files exist on Kolibri Studio...")
      file_diff = tree.get_file_diff(files_to_diff)
      return file_diff
docs: get_file_diff: Download files from nodes
          Args:
              tree (ChannelManager): manager to handle communication to Kolibri Studio
          Returns: list of files that are not on Kolibri Studio