Automating BOM with sub-assemblies and parts

Good day everybody. I have a large assembly for which i want to produce a 2-D drawing. I have a certain predefined BOM structure which I want to automate.

In doing so I am currently facing problems. the problem is something like this:

Lets say I have parts A, B and C. I am making sub assemblies with A and B and naming it X1. With this X1 and part C  I am making another sub assembly and naming it Y1.

Now In the main assembly there are 3 such Y1 sub assemblies. I want only X1 sub-assembly and part C to appear in my BOM. Is there any way to do that???

I am currently using Solidworks 2015.

Please let me know if any kind of further clarification is required. Any help is much appreciated.

Thanks in advance.