I believe it can be done readily in Word but I don't know any easy way in Excel. Even if you format the cells as text, it will still sort 1.10 before 1.2

As always, there are more than one way to skin a cat.

How about having 1.01 rather than 1.1?

Or you could set put each level in its own column, sort these, and concatenate them in a display column.