Keyboard shortcut for fill down of a non-formula?

Hi. I'm trying to manually input a set of data that looks something like this:

7

7.1

7.2

7.2.1

7.2.2

7.2.3

7.3

8

8.1

etc.

I'm looking for a keyboard shortcut to fill down like dragging the corner box does (i.e. if I have 9.2.1 and drag down, it will go 9.2.2, 9.2.3, etc). CTRL+D only copies the cell above and does not advance the number. Is there a setting somewhere to change how that behaves?

I have about 1,000 rows to do, so grinding it out is an option, but keyboard shortcuts will make this faster.