diff --git a/term_reference_tree.js b/term_reference_tree.js
index 319312f..c19eeb0 100644
--- a/term_reference_tree.js
+++ b/term_reference_tree.js
@@ -2,7 +2,7 @@
   Drupal.behaviors.termReferenceTree = {
     attach: function(context, settings) {
       // Bind the term expand/contract button to slide toggle the list underneath.
-      $('.term-reference-tree-button', context).click(function() {
+      $('.term-reference-tree-button:not(.term-reference-tree-button-processed)', context).addClass('term-reference-tree-button-processed').click(function() {
         $(this).toggleClass('term-reference-tree-collapsed');
         $(this).siblings('ul').slideToggle('fast');
       });