I have a dataframe like this

```
  Temp time[s] 
0 20    0
1 21    1
2 21.5  2

```

I want to repeat the dataframe but add the timestamp, my output should like this ,

```
Temp time[s] 
0 20    0
1 21    1
2 21.5  2
3 20    3
4 21    4
5 21.5  5

```

I tried something like this , but didn't worked for me

```
df2 = pd.concat([df]*2, ignore_index=True)
df2['time[s]'] = df2.groupby(level=0).cumcount() * 1

```

Can anyone help me plz ?