add protobuf
diff --git a/demo/digesttreeviewer.cpp b/demo/digesttreeviewer.cpp
index cb52a9e..631ab92 100644
--- a/demo/digesttreeviewer.cpp
+++ b/demo/digesttreeviewer.cpp
@@ -7,4 +7,6 @@
 {
   DigestTreeScene *scene = new DigestTreeScene(this);
   setScene(scene);
+  scene->plot();
+  scene->plot();
 }