I have a dataframe with double index, it looks like this:

```
bal:

                    ano             unit period
business_id id                                 
9564        302    2012            reais  anual
            303    2011            reais  anual
2361        304    2013            reais  anual
            305    2012            reais  anual
2369        306    2013            reais  anual
            307    2012            reais  anual

```

I have another dataframe that looks like this:

```
accounts:

                           A                     B
id                                                                      

302               5964168.52          1.097601e+07
303               5774707.15          1.086787e+07
304               3652575.31          6.608469e+06 
305                321076.15          6.027066e+06
306               3858137.49          9.733126e+06

```

I want to merge them so they look like this:

```
                    ano             unit period              A                     B
business_id id                                 
9564        302    2012            reais  anual     5964168.52          1.097601e+07
            303    2011            reais  anual     5774707.15          1.086787e+07
2361        304    2013            reais  anual     3652575.31          6.608469e+06
            305    2012            reais  anual      321076.15          6.027066e+06
2369        306    2013            reais  anual     3858137.49          9.733126e+06 

```

What I'm trying to do is something like this:

```
bal=bal.merge(accounts,left_on='id', right_index=True)

```

However I think that the synthax is not correct, since I'm getting a ValueError:

```
ValueError: len(right_on) must equal the number of levels in the index of "left"

```

Can anyone help?