code: def save_bert(self, filename: str):
      return torch.save(self.bert_encoder.state_dict(), filename)
  
imports: import torch
  import torch.nn
  from torch.nn import CrossEntropyLoss, MSELoss
  from turing.utils import TorchTuple
  from pytorch_pretrained_bert.modeling import BertModel
  from pytorch_pretrained_bert.modeling import BertPreTrainingHeads, PreTrainedBertModel, BertPreTrainingHeads
  from pytorch_pretrained_bert.file_utils import PYTORCH_PRETRAINED_BERT_CACHE
label_desc: Use image node_id 8 for calling the BertMultiTask obj's underlying member method code with example usage: obj.save_bert(filename) and returns: torch