[{"_id":ObjectId("5c628eef0f17e108ec305682"),"Boiler":{"Warranty":"Void","Plant_Location":"USA","Asset_Status":"Active","Created_Date":"12 Feb 2019","Asset_Last_Service_Date":"2011-07-23","Asset_SRN":"ASDASDKLj131203-91","Asset_Name":"Pressure Pump","Asset_Manufacturer":"Thompson","Asset_Unit_of_Measurement":"PSI","Asset_Inuse_from":"2013-06-25","Asset_Manufactured_On":"2015-04-23","Modified_Date":"12 Feb 2019","Plant_Name":"KCO","Asset_Location":"China","Description":"ALKSJDJKSA"}},{"_id":ObjectId("5c629d110f17e11b180f9290"),"Boiler":{"Asset_Name":"Heater","Asset_Status":"Active","Description":"asdasd","Created_Date":"12 Feb 2019","Asset_Inuse_from":"2009-04-23","Asset_Manufacturer":"JJSSJ","Asset_Last_Service_Date":"2011-05-20","Plant_Location":"HHJJJOO","Warranty":"ASDASDASD","Asset_Unit_of_Measurement":"QQWWEERRTT","Modified_Date":"12 Feb 2019","Asset_Location":"OIUIOU","Plant_Name":"OIPOIPOI","Asset_SRN":"08321940198","Asset_Manufactured_On":"2010-05-23"}},{"_id":ObjectId("5c62ab1a0f17e112e067aeff"),"Boiler":{"Created_Date":"12 Feb 2019","Asset_Status":"Active","Modified_Date":"12 Feb 2019","Plant_Location":"POEWIRPOIQ","Description":"LJKDSAJFWIOFW","Plant_Name":"LKAJSALKJSD","Asset_SRN":"LKJALKJF","Asset_Name":"VCDCZXCXC","Asset_Manufacturer":"POQEWIRPOWEIR","Warranty":"ASDASDASD","Asset_Last_Service_Date":"2002-12-09","Asset_Unit_of_Measurement":";AKS;DLKS;LDK","Asset_Inuse_from":"2000-09-05","Asset_Location":"KAJFLKSADJF","Asset_Manufactured_On":"2001-11-18"}}]

db.collection.aggregate([{$group:{_id:null,AllBoiler:{$push:"$Boiler"}}},{$project:{_id:0,Boiler:"$AllBoiler"}}])