code: def backward(ctx: Any, *grad_outputs) -> Tuple[Tensor, None, None]:
      return (
          HierarchicalAllToAll.forward(
              None, grad_outputs[0], ctx.comm_grps, ctx.src_rank
          ),
          None,
          None,
      )
  
imports: from typing import Any, Optional, Tuple
  import torch
  import torch.distributed
  from torch import Tensor
  from torch.cuda.amp import custom_bwd, custom_fwd
  from torch.distributed import ProcessGroup
label_desc: Use image node_id 2 for calling the HierarchicalAllToAll obj's underlying member method code with example usage: obj.backward(ctx) and returns: HierarchicalAllToAll,  None,  None