BUG: Series constructor from dictionary drops key (index) levels when not all keys have same number of entries

[ArneBinder]

Pandas version checks

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of pandas.

• I have confirmed this bug exists on the main branch of pandas.

Reproducible Example

import pandas as pd

pd.Series({("l1",):"v1", ("l1","l2"): "v2"})
# Out[30]: 
# l1    v1
# l1    v2
# dtype: object

# the reason is that the Series constructor uses internally MultiIndex.from_tuples in the following way (note that the input is a tuple of tuples!):
pd.MultiIndex.from_tuples((("l1",), ("l1","l2")))
# Out[32]: 
# MultiIndex([('l1',),
#             ('l1',)],
#            )

# compare to the following which produces the expected result:
pd.MultiIndex.from_tuples([("l1",), ("l1","l2")])
# Out[33]: 
# MultiIndex([('l1',  nan),
#             ('l1', 'l2')],
#            )

# Note: this was tested with latest release and current master

Issue Description

When calling the Series constructor with a dict where the keys are tuples, a series with MulitIndex gets created. However, if the number of entries in the keys is not the same, key entries from keys with more than the minimum number get dropped. This is in several ways problematic, especially if this produces duplicated index values / keys which is not expected because it was called with a dict (which has per definition unique keys).

Expected Behavior

The MultiIndex of the new series has nan-padded values.

Installed Versions

INSTALLED VERSIONS

commit : 0691c5c
python : 3.10.16
python-bits : 64
OS : Linux
OS-release : 6.8.0-51-generic
Version : #52~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC Mon Dec 9 15:00:52 UTC 2
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : de_DE.UTF-8
LOCALE : de_DE.UTF-8

pandas : 2.2.3
numpy : 2.2.1
pytz : 2024.2
dateutil : 2.9.0.post0
pip : 24.2
Cython : None
sphinx : None
IPython : None
adbc-driver-postgresql: None
adbc-driver-sqlite : None
bs4 : None
blosc : None
bottleneck : None
dataframe-api-compat : None
fastparquet : None
fsspec : None
html5lib : None
hypothesis : None
gcsfs : None
jinja2 : None
lxml.etree : None
matplotlib : None
numba : None
numexpr : None
odfpy : None
openpyxl : None
pandas_gbq : None
psycopg2 : None
pymysql : None
pyarrow : None
pyreadstat : None
pytest : None
python-calamine : None
pyxlsb : None
s3fs : None
scipy : None
sqlalchemy : None
tables : None
tabulate : None
xarray : None
xlrd : None
xlsxwriter : None
zstandard : None
tzdata : 2024.2
qtpy : None
pyqt5 : None