Aggregation in MongoDB

I have two city and state Collections as follows:

cities

  {
    "_id" : ObjectId("5be385fdb9ee9a25f7e418a9"),
    "ID" : "1",
    "Nome" : "Afonso Cláudio",
    "Estado" : "8"
},{
    "_id" : ObjectId("5be385fdb9ee9a25f7e418aa"),
    "ID" : "2",
    "Nome" : "Água Doce do Norte",
    "Estado" : "8"
}

states

{
    "_id" : ObjectId("5be385feb9ee9a25f7e42e65"),
    "ID" : "1",
    "Sigla" : "AC",
    "Nome" : "Acre"
}

I want to create a new collection from these two. For this I wrote the following query

db.cidades.aggregate([
{ $lookup: { from:"estados",localField: "Estado",foreignField: "ID",as:"estado"}}, 
{ $sort :  { Estado:1,Nome:1 }},
{ $project:{ "ID":0,"_id":0,"Estado":0,"estado.ID":0,"estado._id":0}},
{ $addFields: { "cnpj": null,"legislacao": [] }},
{ $out : "municipios" }    
]).pretty()

What gave me the following result:

{
    "_id" : ObjectId("5be5c6407608e1137ab33fe4"),
    "Nome" : "Acrelândia",
    "estado" : [ 
        {
            "Sigla" : "AC",
            "Nome" : "Acre"
        }
    ],
    "cnpj" : null,
    "legislacao" : []
}

What I would really like is the end result looks like this:

{
    "_id" : ObjectId("5be5c6407608e1137ab33fe4"),
    "Nome" : "Acrelândia",
    "Sigla" : "AC",
    "Nome" : "Acre"
    "cnpj" : null,
    "legislacao" : []
}

or so:

{
    "_id" : ObjectId("5be5c6407608e1137ab33fe4"),
    "Nome" : "Acrelândia",
    "estado" :{
            "Sigla" : "AC",
            "Nome" : "Acre"
        }
    ,
    "cnpj" : null,
    "legislacao" : []
}

What modifications should I make in the query to get the above result?