foo.js

App.Folder = DS.Model.extend({
    name: DS.attr('string'),
    parentFolder: DS.belongsTo('App.Folder'),
    childrenFolders: DS.hasMany('App.Folder'),
    files: DS.hasMany('App.File'),

    elements: function() {
        // Concatenate files and childrneFolders

        return result;
    }.property('files', 'childrenFolders')
});


App.FolderController = Ember.ObjectController.extend({
    createFolder: function() {
        this.get('content.childrenFolders').createRecord({
            name: 'bar',
            parentFolder: this.get('content')
        });
    }
});