code: function handleTreeToggle(index, element) {
    var parentItem = $(element).parent();
    var collapsing = parentItem.hasClass('expandable');
    if (collapsing) {
    } else {
      // When expanded be sure the pipeline and its children are showing.
      scrollTreeToPipeline(parentItem);
    }
  }
docs: Handles when the user toggles a leaf of the tree.