В dataFrame есть дополнительный столбец идентификатора, считанный из csv

Я создал dataFrame и это вывод:

print(train_df)

           author                                               text
0   BernardHickey  The Commmonwealth Bank of Australia (CBA) warn...
1   BernardHickey  Rupert Murdoch predicted in a newspaper interv...
2   BernardHickey  News Corp Ltd chairman and chief executive Rup...
3   BernardHickey  Rupert Murdoch on Tuesday reported that News C...
4   BernardHickey  Rupert Murdoch on Tuesday reported that News C...

Затем я сохранил фрейм данных:

train_df.to_csv(data_path+'/train.csv')

Когда я прочитал это снова:

data = pd.read_csv(data_path+'/train.csv')
data.head(10)

Unnamed: 0  author  text
0   0   BernardHickey   The Commmonwealth Bank of Australia (CBA) warn...
1   1   BernardHickey   Rupert Murdoch predicted in a newspaper interv...
2   2   BernardHickey   News Corp Ltd chairman and chief executive Rup...
3   3   BernardHickey   Rupert Murdoch on Tuesday reported that News C...

Почему там столбец Unnamed? Как я могу этого избежать?