Best way to create Indented Bill Of Material

Jonathan_Wilkof 

If you can define a maximum number of levels, you could set-up a fairly simple query that merges  itself a number of time with itself, as demonstrated in the attached workbook.

With an infinite number of levels of sub parts, though, you'll need something better, but that will not be very straight-forward. See link below.

https://techcommunity.microsoft.com/t5/excel/parent-child-flattening-multiple-levels/m-p/2744756