How to fill an array in given format?

I want to form an array like this:

$routes = [
            array("key" => 0, "title" => "All"),
            array("key" => 1, "title" => "Web Series"),
            array("key" => 2, "title" => "Reality Shows"),
            array("key" => 3, "title" => "Singing"),
            array("key" => 4, "title" => "Vendors")
        ];

Here, the titles (web series, reality shows, singing) should come as a response from database:

    $projectTypes = ProjectType::select('project_type_title')->get()->all();

How to populate an array like above using these values ?

Note:

array("key" => 0, 
      "title" => "All") 

must be predefined and not fetched from database only other project types are fetched from the database

via Chebli Mohamed