       throw new Error 'Invalid parent group' if parentGroupElement.tagName != 'LI' or ! parentGroupElement.classList.contains 'group'
       parentGroupElement = parentGroupElement.nextSibling
     else
-      parentGroupElement = @treeRoot
+      parentGroupElement = @_treeRoot
 
     element.classList.add type
     element.draggable = true

      while removedSelectedItems.length > 0
        removedSelectedItem = removedSelectedItems[removedSelectedItems.length - 1]
        @selectedItems.splice @selectedItems.indexOf(removedSelectedItem), 1

      element.parentElement.removeChild childrenElement


        event.target.parentElement.classList.toggle 'collapsed'
        return

    # Set selection
    @clearSelection() if ! event.shiftKey and ! event.ctrlKey

    element = event.target
    while element.tagName != 'LI' or (! element.classList.contains('item') and ! element.classList.contains('group'))
      return if element == @_treeRoot
      element = element.parentElement

    if @selectedItems.length > 0
      return if @selectedItems[0].parentElement != element.parentElement

    if event.shiftKey and @selectedItems.length > 0
      startElement = @_firstSelectedItem
      elements = []
      inside = false

