Thanks @Asya_Kamsky. Yeah as you said the infinite depth is not a good idea and unknown depth is a better name. To explaining the question, I should say that we have _id of object that its name is item6 so all the things we have is a _id that is ObjectId("53bd7837156aa38914f55176"). I am sorry that asked so bad with mistake typing of _id.
The purpose of query is to getting (project) the item6 when we dont have level and depth of item6. we just want to mapping or unwinding all items to match _id and then project that. Thanks