New Twiddle

adapters.application.js

import DS from 'ember-data';
export default DS.JSONAPIAdapter.extend({  
});

components.tree-node.js

import Ember from 'ember';

export default Ember.Component.extend({
  
  datasource: Ember.A(),
  
  tagName: 'ul',
  itemTag: 'li',
  itemClass: 'item',
  itemOpenedClass: 'item--open',

  parent: null,
  childItems: Ember.A(),
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
});

helpers.eq.js

import Ember from 'ember';

const eq = (params) => params[0] == params[1];

export default Ember.Helper.helper(eq);

models.category.js

import Model from "ember-data/model";
import attr from "ember-data/attr";
import { belongsTo, hasMany } from "ember-data/relationships";

export default Model.extend({
  title: DS.attr('string'),
  parent: DS.belongsTo('category', {inverse: 'children'}),
  children: DS.hasMany('category', {inverse: 'parent'})
});

router.js

import Ember from 'ember';
import config from './config/environment';

const Router = Ember.Router.extend({
  location: 'none',
  rootURL: config.rootURL
});

Router.map(function() {
  this.route('main', { path: '/' });
});

export default Router;

$.mockjax({
      url: '/categories',
      type: 'GET',
      status: '200',
      dataType: 'json',
			responseText: {
        "data": [
          {
            "type": "categories",
            "id": 1,
            "attributes": {
              "title": "Category 1",
            },
            "relationships": []
          },
          {
            "type": "categories",
            "id": 2,
            "attributes": {
              "title": "Category 2"
            },
            "relationships": {
              "parent": {
                "data": {
                  "type": "categories",
                  "id": 1
                }
              }
            }
          },
          {
            "type": "categories",
            "id": 3,
            "attributes": {
              "title": "Category 3"
            },
            "relationships": {
              "parent": {
                "data": {
                  "type": "categories",
                  "id": 2
                }
              }
            }
          }
        ]
      }
    });

routes.main.js

import Ember from 'ember';

export default Ember.Route.extend({
  model() {
    return this.get('store').findAll('category');
  }
});

templates.application.hbs

{{log model}}

{{#tree-node datasource=model as |item|}}
	{{#link-to '/' item.id}}
  	{{item.title}}
	{{/link-to}}
{{/tree-node}}

templates.components.tree-node.hbs

{{#each datasource as |dataitem|}}
    {{#if (eq dataitem.parent.id parent) }}
        {{#tree-item register-as=this.childItems item=dataitem tagName=itemTag className=itemClass classOpened=itemOpenedClass classActive=itemActiveClass}}

            {{yield this dataitem }}

            {{#if dataitem.children}}
                {{#tree-node parent=dataitem.id active=active actionsList=actionsList datasource=dataitem.children as |target subitem| }}
                    {{yield target subitem}}
                {{/tree-node}}
            {{/if}}

        {{/tree-item}}
    {{/if}}
{{/each}}

twiddle.json

{
  "version": "0.10.7",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.10.0",
    "ember-data": "2.3.3",
    "ember-template-compiler": "2.10.0",
    "ember-testing": "2.10.0",
    "jquery-mockjax": "https://cdnjs.cloudflare.com/ajax/libs/jquery-mockjax/1.6.2/jquery.mockjax.js"
  },
  "addons": {}
}