code: def _broadcast_to_and_flatten(
      tree: PyTree,
      treespec: TreeSpec,
      is_leaf: Optional[Callable[[PyTree], bool]] = None,
  ) -> Optional[List[Any]]:
      assert isinstance(treespec, TreeSpec)
      full_tree = tree_unflatten([0] * treespec.num_leaves, treespec)
      try:
          return broadcast_prefix(tree, full_tree, is_leaf=is_leaf)
      except ValueError:
          return None
  
imports: import functools
  import warnings
  from typing import Any, Callable, Iterable, List, Optional, overload, Tuple, Type, TypeVar, Union
  import torch
  import optree
  from optree import PyTreeSpec
label_desc: Use image node_id 35 for calling a global function with example usage: _broadcast_to_and_flatten(tree, treespec, is_leaf) and returns: broadcast_prefix, None