docstr: save wscorpus to files
  
  :param str folder: path to directory
  :type folder: string
  :param str format: either TEXT or COLUMN
  :type format: str
code: def save(self, folder, format):
      """save wscorpus to files
  
      :param str folder: path to directory
      :type folder: string
      :param str format: either TEXT or COLUMN
      :type format: str
      """
      try:
          mkdir(folder)
      except Exception:
          pass
      for document in self.documents:
          f = join(folder, document.id)
          content = "\n".join(document.sentences)
          write(f, content)
  
file_path: underthesea/underthesea/corpus/ws_corpus.py
imports: import io
  from underthesea.corpus import Document, UnicodeTransformer, Corpus
  from os import listdir, mkdir
  from os.path import join
  from underthesea.util.file_io import write
label_desc: Use image node_id 5 for calling the WSCorpus obj's underlying member method code with example usage: obj.save(folder, format) without return types