How to export from excel and in what format?

Question

SQL

There is a list of articles in excel, distributed by levels. In accordance with the level, there are indents of different lengths from the edge.

I need to number all these articles (and there are 3000+). The numbering should also be hierarchical, like this:

I don't want to do it by hand.
Does anyone have any ideas? In what and in what format can the excel be uploaded in order to somehow indicate the indents? To then write a process, for example, in SQL (or on the same Excel) automatically numbering?
The problem is that the indents from the edge are not fixed in any way, and if you save, for example, in CSV, then all the indents disappear. The same is true for simple copying to another sheet or file. As I understand it, the indents are formed by Excel itself specifically in this sheet, since there is a grouping by levels. There are no spaces in the lines.