Google-apps-script – Google App Script DriveApp get top level parent of a file

I want to know how to find out the top level directory parent of a file (which resides under "My Drive"). Files are stored under multi-level sub-folders.

Since I have the same file stored in multiple places, I want to make sure that the source of the file that I am picking up is the right one. I have made a really dirty hack, which is time consuming which looks like this:

function start() {
    var files = DriveApp.searchFiles("(title contains 'Worksheet')");
    while (files.hasNext()) {
      var file = files.next();
      var fileName = file.getName();
      var whichParents = getAllParents(file);
      // process whichParents to use indexOf to look for a substring in retStr and move forward.
}

function getAllParents(file) {
  var retStr="";
  try{
    var folder;
    var parents = file.getParents();
    while(1) {
      while (parents.hasNext()) {
      var parent = parents.next();
      folder=parent;
      retStr = retStr + parent.getName() + "->";
      if(parent.getName() == "My Drive")
        throw Exception;
      }
      parents = folder.getParents();
    }
  }
  catch(e){
    return retStr;    
  }
}

I have looked through StackExchange for quite some time to figure out why an exception is generated, to no avail. Appreciate any help on this!