Pumping WHILE breastfeeding??

Does anyone pump one side while baby feeds on other and just alternate sides the next feeding and so on? Figured this way i could start a small stash for when i'm not with baby and breastfeed at the same time. I understand you want to establish breastfeeding before giving a bottle and I plan to, i'm talking about for later on. Is this technique a thing? Im a ftm and kind of want to do a combination of pumping/bfing but not sure how.