Automatic & Dynamic Row Numbering For Outline Numbers Like #.#.#

I would like to ask for some assistance to my Spreadsheet problem.

To illustrate my problem please see below:

1------------> Level 1
1.1----------> Level 1 Sublevel 1
1.1.1--------> Level 1 Sublevel 1 Item 1
1.1.2--------> Level 1 Sublevel 1 Item 2
1.2----------> Level 1 Sublevel 2
1.2.1--------> Level 1 Sublevel 2 Item 1
1.2.2
2
2.1
2.1.1
2.1.1
2.2
and so on

I need to have a formula to automate the adding of outline numbers from "Level 1, Sublevel 1, Item 1..." So that if I deleted or added a row, the rest will automatically update themselves.

I will be the one manually inputing the Top Level and Sublevels I just need that the Items will be automatically added and computed basing from the previous level.

What I am planning to do is:
1. Check previous cell if the format has two decimal points or periods --> kinda stuck here

2. If there's only one then it will be the Sublevel 1 Item 1 (or depending to its location)

3. If there's already two periods "." then it will compute automatically for what item it is already.
ie:

1
1.1
1.1.1
1.1.2----->Checks the previous cell if it has 2 decimal places then if it does then it will add 1