[{"_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([{$set:{modelYear:{$arrayToObject:{$map:{input:"$model",as:"model",in:["$$model.modelCode","$$model.modelYearListing"]}}}}},{"$unwind":"$model"},{"$group":{"_id":{"modelName":"$model.modelName"},"modelYearListing":{"$addToSet":"$modelYear"}}},{"$unwind":"$modelYearListing"},{"$group":{"_id":{"modelCode":"$_id.modelCode","modelName":"$_id.modelName","model":"$modelYear"},"modelYearListing":{"$push":"$modelYearListing"}}},{"$project":{"modelCode":"$_id.modelCode","modelName":"$_id.modelName","modelYearListing":1,"model":"$_id.model","_id":0}}])