Feature request

Maybe it is a weird idea, but we can provide a new interface for "flat" representation of a nested series within NestedFrame, using dot-prefix:

ndf["nested."] = flat_with_the_matched_index
assert_frame_equal(ndf["nested."], flat_with_the_matched_index)

It would simplify flattening and nesting (no add_nested) in simple cases.

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Please check the following:

• I have described the purpose of the suggested change, specifying what I need the enhancement to accomplish, i.e. what problem it solves.
• I have included any relevant links, screenshots, environment information, and data relevant to implementing the requested feature, as well as pseudocode for how I want to access the new functionality.
• If I have ideas for how the new feature could be implemented, I have provided explanations and/or pseudocode and/or task lists for the steps.