Show files in Broccoli-tree?

My Ember-CLIs vendor.js is taking up way too much space. Therefore I'd like to be able to see which files go into its Brocolli-tree.

I tried http://ift.tt/1EuJxJ0 and added this to my Brocfile.js but upon launching ember serve nothing is output

var loggedApp = log(app.toTree(), { output: 'tree', label: 'my-app-name tree' });

module.exports = app.toTree();