MultiIndex.from_tuples returns an Index when all tuples are length 1

In [1]: import pandas as pd
In [2]: pd.MultiIndex.from_tuples([('a',), ('b',)])
Out[2]: Index(['a', 'b'], dtype='object')

This should return a MultiIndex I think, like

Out[5]:
MultiIndex(levels=[['a', 'b']],
           labels=[[0, 1]])

Well, pd.MultiIndex([['a', 'b']], [[0, 1]]) returns the same thing as from_tuples (an index) so maybe this is intentional.

Trying to figure out if this is intentional or not (this came up in my categorical dtype refactor).

[jbrockmendel]

+1 for having MultiIndex.from_whatever consistently return a MultiIndex.

[TomAugspurger]

#14823 seems unrelated, unless I’m missing something These are all the same length (1).

The fix is essentially a one-liner: https://github.com/pandas-dev/pandas/compare/master...TomAugspurger:multiindex-squeeze?expand=1#diff-4ffd1c69d47e0ac9f2de4f9e3e4a118cR102