https://github.com/emberjs/data/issues/5159

adapters.application.js

import Adapter from "ember-data/adapters/rest";

export default Adapter.extend();

initializers.pretender.js

export function returnJSON(status, body) {
  return json(...arguments);
};

export function json(status, body) {
  if (arguments.length === 1) {
    body = status;
    status = 200;
  }
  
  return [
    status,
    { "Content-Type": "application/json" },
    JSON.stringify(body)
  ];
};

export const server = new Pretender();

export function initialize() {
  server.handledRequest = function(verb, path, request) {
    console.log(`handled request to ${verb} ${path}`);
  }

  server.unhandledRequest = function(verb, path, request) {
    console.log(`undhandled request ${verb} ${path}`);
  }
};

export default {
  name: 'pretender',
  initialize
};

models.node.js

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

export default Model.extend({
  name: attr(),
  parent: belongsTo('node', { inverse: 'children' }),
  children: hasMany('node', { inverse: 'parent' })
});

routes.application.js

import Ember from 'ember';
import { server, json } from '../initializers/pretender';

server.map(function() {
  this.get('/nodes', function() {
    return json({
      nodes: [
{  
   "id": "1",
   "name":"D3",
   "children":[  
      {  
         "id": "c1",
         "name":"Drivers",
         "children":[  
            {  
               "id": "c1-1",
               "name":"JavaScript",
               "size":17010
            },
            {  
               "id": "c1-2",
               "name":"SVG",
               "size":5842
            },
            {  
               "id": "c1-3",
               "name":"CSS",
               "size":5842
            },
            {  
               "id": "c1-4",
               "name":"Also HTML",
               "size":5842
            }
         ]
      },
      {  
          "id": "c2",
          "name":"Animation",
          "children":[  
             {  
                "id": "c2-1",
                "name":"CSS3 Transitions",
                "children":[  
                   {  
                      "id": "c2-1-1",
                      "name":"Chaining",
                      "size":3938
                   },
                   {  
                      "id": "c2-1-2",
                      "name":"Tweening",
                      "size":3938
                   }
                ]
            }
         ]
       },
   ]
}
]});
  });
});

export default Ember.Route.extend({
  model: function() {
    return this.store.query('node', {});
  }
});

serializers.application.js

import DS from "ember-data";
import Serializer from "ember-data/serializers/rest";

export default Serializer.extend(DS.EmbeddedRecordsMixin, {
  attrs: {
    children: {
      embedded: 'always'
    }
  }
});

templates.application.hbs

<ul>
{{#each model as |node|}}
  <ul>
	  <li>Name: {{node.name}}</li>
    <li>Children: {{node.children.length}}</li>
    <li>
      <ul>
        {{#each node.children as |node|}}
          <li>Name: {{node.name}}</li>
        {{/each}}
      </ul>
    </li>
  </ul>
{{/each}}
</ul>

twiddle.json

{
  "version": "0.10.4",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "release",
    "ember-data": "release",
    "ember-template-compiler": "release",
    "route-recognizer": "https://rawgit.com/tildeio/route-recognizer/56f5fcec6ae58d8e86b5dc77609809fb91198142/dist/route-recognizer.js",
    "FakeXMLHttpRequest": "https://rawgit.com/pretenderjs/FakeXMLHttpRequest/23c3a96b5b24f1bfe595867437e4f128a29c2840/fake_xml_http_request.js",
    "pretender": "https://rawgit.com/pretenderjs/pretender/c6de9afe18b1472aded2592f5a80ad9a26a0e262/pretender.js"
  },
  "addons": {}
}