Stats tree seems to work properly, including pruning of "empty" leaves
diff --git a/utils/trie.h b/utils/trie.h
index 51a7678..dbd3e1d 100644
--- a/utils/trie.h
+++ b/utils/trie.h
@@ -377,6 +377,11 @@
   {
     payload_ = payload;
   }
+
+  Key key () const
+  {
+    return key_;
+  }
   
   inline void
   PrintStat (std::ostream &os) const;