[{"_id":"ENVD","model":[{"modelCode":"Z34L","modelName":"370Z","modelYearListing":"2009 - Present"},{"modelCode":"Z35L","modelName":"370Z","modelYearListing":"2010 - Present"}]},{"_id":"ENVD2","model":[{"modelCode":"Z36L","modelName":"370Z","modelYearListing":"2008 - Present"},{"modelCode":"Z34L","modelName":"370Z","modelYearListing":"2009 - Present"}]}]

db.collection.aggregate([{"$unwind":"$model"},{"$group":{"_id":{"modelName":"$model.modelName"},"modelYearListing":{"$addToSet":{k:"$model.modelCode",v:"$model.modelYearListing"}}}},{"$project":{_id:0,"modelName":"$_id.modelName",modelYear:{"$arrayToObject":"$modelYearListing"}}}])