Ember: How to merge an UnwatchedDir with a tree / unwatch a subdirectory?

Question

I want a subdirectory of a directory (say public) to be unwatched for changes.

In order to unwatch a directory itself, in my ember-cli-build.js, I'm doing app.trees.public = new UnwatchedDir('public') before return.

But how can I unwatch only a subdirectory inside public?

I did the below, but doesn't work.

var publicMinusLocales = new Funnel('public', { exclude: ['assets/locales'] });
var unwatchedLocalesTree = new Funnel(new UnwatchedDir('public/assets/locales'));
var mergedTree = new BroccoliMergeTrees([publicMinusLocales, unwatchedLocalesTree], { overwrite: true })
app.trees.public = mergedTree;