code: def process_tree(self, channel_node):
          
          file_names = []
          self.process_tree_recur(file_names, channel_node)
          return [x for x in set(file_names) if x]
docs: Returns a list of all file names associated with a tree. Profiling suggests using a global list with `extend`
          is faster than using a global set or deque.
          :param channel_node: Root node of the channel being processed
          :return: The list of unique file names in `channel_node`.