Cannot write MultiIndex DataFrame to excel (to_excel) which contains Peroid IntervalIndex
#### Code Sample, a copy-pastable example if possible

```python
import pandas as pd
import numpy as np

midx = pd.MultiIndex.from_arrays(
    [
        np.repeat([1, 2], 2),
        pd.interval_range(start=pd.Timestamp("2020-01-01"), periods=4, freq="6M"),
    ]
)

df = pd.DataFrame(data=np.random.randint(0, 2, size=(4,)), index=midx)
print(df)

df.to_excel("tmp.xlsx")
```
#### Problem description
I receive a TypeError and the DataFrame does not write to file.

```python
...
  File "pandas/_libs/tslibs/timestamps.pyx", line 412, in pandas._libs.tslibs.timestamps.Timestamp.__new__

  File "pandas/_libs/tslibs/conversion.pyx", line 329, in pandas._libs.tslibs.conversion.convert_to_tsobject

TypeError: Cannot convert input [True] of type <class 'bool'> to Timestamp
```

#### Expected Output
Expect the DataFrame to write to file. A DataFrame with a Period/IntervalIndex alone can be written to an excel file. Seems to be an issue with MultiIndex.
#### Output of ``pd.show_versions()``

<details>
INSTALLED VERSIONS
------------------
commit           : None
python           : 3.7.4.final.0
python-bits      : 64
OS               : Linux
OS-release       : 5.4.7-200.fc31.x86_64
machine          : x86_64
processor        : x86_64
byteorder        : little
LC_ALL           : None
LANG             : en_GB.UTF-8
LOCALE           : en_GB.UTF-8

pandas           : 0.25.3
numpy            : 1.17.2
pytz             : 2019.3
dateutil         : 2.8.1
pip              : 19.2.3
setuptools       : 41.4.0
Cython           : 0.29.13
pytest           : 5.2.1
hypothesis       : 4.54.2
sphinx           : 2.2.0
blosc            : None
feather          : None
xlsxwriter       : 1.2.1
lxml.etree       : 4.4.1
html5lib         : 1.0.1
pymysql          : None
psycopg2         : None
jinja2           : 2.10.3
IPython          : 7.8.0
pandas_datareader: None
bs4              : 4.8.2
bottleneck       : 1.3.1
fastparquet      : None
gcsfs            : None
lxml.etree       : 4.4.1
matplotlib       : 3.1.1
numexpr          : 2.7.0
odfpy            : None
openpyxl         : 3.0.0
pandas_gbq       : None
pyarrow          : 0.13.0
pytables         : None
s3fs             : None
scipy            : 1.3.2
sqlalchemy       : 1.3.9
tables           : 3.6.1
xarray           : None
xlrd             : 1.2.0
xlwt             : 1.3.0
xlsxwriter       : 1.2.1
</details>
