[{_id:1,from:"from1",to:"to1"},{_id:2,from:"from1",to:"to2"},{_id:3,from:"from2",to:"to1"},{_id:4,from:"from1",to:"to3"},{_id:5,from:"from2",to:"to2"},{_id:6,from:"from3",to:"to1"}]

db.collection.aggregate([{"$facet":{"query1":[{$match:{"from":{"$in":["from1","from3"]/** <- Match Query One*/}}},{$group:{_id:null,tos:{$push:"$to"}}}],"query2":[{$match:{"from":{"$in":["from2"]/** <- Match Query Two*/}}},{$group:{_id:null,tos:{$push:"$to"}}}]}},{"$unwind":"$query1"},{"$unwind":"$query2"},{"$project":{toIntersection:{"$setIntersection":["$query1.tos","$query2.tos"]}}}])