code: def flattened(trials_tree: TreeNode[T]) -> list[T]:
      """Get a list of the tree items in pre-order traversal"""
      return [node.item for node in trials_tree]
  
imports: from __future__ import annotations
  from typing import Callable, Generic, Iterable, Iterator, Sequence, TypeVar
label_desc: Use image node_id 3 for calling a global function with example usage: flattened(trials_tree) and returns: unknown