Automatic numbering in Excel with hierarchy

I would like to do an automatic summary numbering. The only thing we could do is to number the A's (the titles) but the subtitles should be numbered automatically. If the title = 1, subtitle 1.1, below 1.1.1 and so on.

Let's say the titles are A, B and C are subtibles.

The pattern should be like this

1.A

1.1 B

1.2 B

2.A

2.1 B

2.1.1 C

So I tried this : https://stackoverflow.com/a/32321112/7968011

What I get

What we want

What we want

If you have your Level Marker as "A" / "B" / "C" in Column A, and the heading in Column B, then you can use the following (convoluted) code:

=REPT(CHAR(9), CODE(A1)-65) & SUMPRODUCT(--(A:A="A")*--(ROW(A:A)<=ROW(A1))) & "." & IF(CODE(A1)>65,SUMPRODUCT(--(A:A="B")*--(ROW(A:A)<=ROW(A1))*--(ROW(A:A)>=MAX(--ROW(A:A)*--(A:A="A")*--(ROW(A:A)<=ROW(A1))))) & ".","") & IF(CODE(A1)>66,SUMPRODUCT(--(A:A="C")*--(ROW(A:A)<=ROW(A1))*--(ROW(A:A)>=MAX(--ROW(A:A)*--(A:A="B")*--(ROW(A:A)<=ROW(A1))))) & ".","") & CHAR(9) & B1

Let's break it down into steps:

1. Start with Tabs to indent the heading (0 for "A", 1 for "B", 2 for "C"): REPT(CHAR(9), CODE(A1)-65) where Char(9) is a Tab.

2. Next, we want to count how many "A"s have we had. We can use SUMPRODUCT to run this as an Array Formula, looking for cells where the value is "A" and the Row is <= current row: SUMPRODUCT(--(A:A="A")*--(ROW(A:A)<=ROW(A1))). Shove a dot after that, and you have your heading number.

3. Next, IF Column A is "B" or later in the alphabet (IF(CODE(A1)>65, since CODE("A")=65, CODE("B")=66, etc) then we want to count how many "B"s since the last "A". This is very similar to our last query, but we need a ROW(A:A)>=LAST_A. But, what is LAST_A? Well, we want the MAX Row where Column A = "A" and Row <= current row. So, MAX(--ROW(A:A)*--(A:A="A")*--(ROW(A:A)<=ROW(A1))).

4. This gives SUMPRODUCT(--(A:A="B")*--(ROW(A:A)<=ROW(A1))*--(ROW(A:A)>=MAX(--ROW(A:A)*--(A:A="A")*--(ROW(A:A)<=ROW(A1)))))

Now, we need to add the IF and the full-stop, to get

If(Code(A1)>65,SUMPRODUCT(--(A:A="B")*--(ROW(A:A)<=ROW(A1))*--(Row(A:A)>=MAX(--ROW(A:A)*--(A:A="A")*--(ROW(A:A)<=ROW(A1))))) & ".","")

Repeat the same for all "C"s since the last "B", and then finally add a Tab (CHAR(9)) and the value in Column B.

(If you want, for example, 4 spaces or 6 hyphens or 7 dots instead of Tabs at the start of the row or between the number and the tile, just replace the first or last CHAR(9))

{EDIT} Example: