code: def _write_cat_column(self, worksheet, col, level, num_format):
          
          worksheet.set_column(col, col, 10)  # wide enough for a date
          for off, name in level:
              row = off + 1
              worksheet.write(row, col, name, num_format)
docs: Write a category column defined by *level* to *worksheet* at offset
          *col* and formatted with *num_format*.