Register unique embedded documents

I want to add an embedded document, I am using $push of update, in schema I put the attribute as index: { unique : true } , but not respecting the rule this is registering item as the same name

Can anyone help me?

var funcionario = new Schema({
    nome : { type : String, index : { unique : true } }
});

var empresa = new Schema({
    nome : { type : String },
    funcionario : [ funcionario ]
});