BUG: pandas.read_excel creates a DataFrame with incorrect multi-level columns
- [x] I have checked that this issue has not already been reported.

- [x] I have confirmed this bug exists on the latest version of pandas.

- [ ] (optional) I have confirmed this bug exists on the master branch of pandas.

---

**Note**: Please read [this guide](https://matthewrocklin.com/blog/work/2018/02/28/minimal-bug-reports) detailing how to provide the necessary information for us to reproduce your bug.

There is a file a.xlsx with only index and multi-level columns:
<img width="547" alt="image" src="https://user-images.githubusercontent.com/33289453/82064630-9e025000-96ff-11ea-8f59-278622c2202a.png">
```pd.read_excel('a.xlsx', index_col=0, header=[0, 1])``` creates a DataFrame with incorrect multi-level columns:
<img width="502" alt="image" src="https://user-images.githubusercontent.com/33289453/82058218-06006880-96f7-11ea-8098-879220a4e88c.png">

However, if the file b.xlsx with the same structure (shown below) is not empty, the result appears to be correct:
<img width="568" alt="C559F1A1-36E2-4B1E-B6EF-8AD1EDAE7420" src="https://user-images.githubusercontent.com/33289453/82063866-9c845800-96fe-11ea-85c4-7848d83a0ab1.png">
<img width="598" alt="image" src="https://user-images.githubusercontent.com/33289453/82063912-aa39dd80-96fe-11ea-844f-2b7ff2156b19.png">



#### Problem description

The parameter ```header=[0, 1]``` indicates that the first two rows of the excel file should be used as multi-level columns, but the result got first three rows as the multi-level columns.

#### Expected Output
```pd.read_excel('a.xlsx', index_col=0, header=[0, 1])``` should get the DataFrame:
<img width="293" alt="image" src="https://user-images.githubusercontent.com/33289453/82059223-4e6c5600-96f8-11ea-8363-c829d43324db.png">



#### Output of ``pd.show_versions()``

<details>

INSTALLED VERSIONS
------------------
commit           : None
python           : 3.8.2.final.0
python-bits      : 64
OS               : Darwin
OS-release       : 19.4.0
machine          : x86_64
processor        : i386
byteorder        : little
LC_ALL           : None
LANG             : None
LOCALE           : None.UTF-8

pandas           : 1.0.3
numpy            : 1.18.1
pytz             : 2020.1
dateutil         : 2.8.1
pip              : 20.0.2
setuptools       : 46.2.0.post20200511
Cython           : None
pytest           : None
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : None
psycopg2         : None
jinja2           : 2.11.2
IPython          : 7.13.0
pandas_datareader: None
bs4              : None
bottleneck       : None
fastparquet      : None
gcsfs            : None
lxml.etree       : None
matplotlib       : 3.1.3
numexpr          : None
odfpy            : None
openpyxl         : 3.0.3
pandas_gbq       : None
pyarrow          : None
pytables         : None
pytest           : None
pyxlsb           : None
s3fs             : None
scipy            : None
sqlalchemy       : None
tables           : None
tabulate         : None
xarray           : None
xlrd             : 1.2.0
xlwt             : 1.3.0
xlsxwriter       : None
numba            : None

</details>
