[{"experience":"0 year"},{"experience":"1 year"},{"experience":"3 years"},{"experience":"5 years"}]

db.collection.aggregate([{$addFields:{regex:{$regexFind:{input:"$experience",regex:"^\\d+"}}}},{$set:{experience_num:{$convert:{input:"$regex.match",to:"int"}}}},{$match:{experience_num:{"$gte":1,"$lte":3}}},{$project:{experience:1}}])