Building Project with portfolio items in rally tree grid

I want to build project team-wise portfolio items

project -1 - Feature -1 - Feature -2

project - 2 - Feature -1 - Feature -2

I am unable to get project and features as children in rally tree builder, I have tried like below:

       Rally.onReady(function() {
        Ext.define('Rally.example.SimpleTreeGrid', {
            extend: 'Rally.app.App',
            componentCls: 'app',

            launch: function() {
                Ext.create('Rally.data.wsapi.TreeStoreBuilder').build({
                    models: ['PortfolioItem/Feature'],
                    autoLoad: true,
                    enableHierarchy: true
                }).then({
                    success: this._onStoreBuilt,
                    scope: this
                });
            },

            _onStoreBuilt: function(store) {
                this.add({
                    xtype: 'rallytreegrid',
                    store: store,
                    context: this.getContext(),
                    enableEditing: false,
                    enableBulkEdit: false,
                    shouldShowRowActionsColumn: false,
                    enableRanking: false,
                    childEls: ["title"],
                    columnCfgs: [
                        'Name',
                        'State',
                        'Owner'
                    ]
                });
            }
        });


        Rally.launchApp('Rally.example.SimpleTreeGrid', {
          name: 'Simple Tree Grid Example'
        });
    });

from Building Project with portfolio items in rally tree grid