mongodb $search two collections holding geoJSON

Question

I am trying to work out how to do $text search on 2 collections at the same time and show them to the end user.

I have a collection called suburbs and a collection call LocalAreas the reason being that local areas are City boundaries while Suburbs are suburbs of that area.

Now lets say I want to type Perth It should lookup both collections for the word Perth

I have added search index on and I know I can do this

for Suburbs I can do this.

[
  {
    $search: {
      index: 'Suburbs',
      text: {
        query: 'Perth',
        path: {
          'wildcard': '*'
        }
      }
    }
  }
]

But how do I do this for both collections at the same time?