I need an advice please

Stephane,

This kind of question seems to pops up all the time about trying to manufacture a profile in advance of getting into b-school.

Rather than repeat myself, I've written something about this:

https://www.mbaapply.com/advice2.htm#forrestgump

In short, you need to build a life, not a resume. Volunteer at non-profits ONLY if you would do it regardless of b-school. Do it because you believe in it, because it'll become apparent that it's just window dressing and resume building. You can't fool anyone, since there will be others who are heavily involved in activities they believe in, and they will have level of commitment and enthusiasm that you simply can't match if your intentions are merely to build a stronger profile. Or here's another way to put it: if you're more focused on trying to manufacture a resume to get into H/S/W more than you are focused on being the most accomplished person you can be in areas of interest that are most meaningful to you -- you won't have a chance of getting in.