diff --git a/library/cwm/src/Makefile.am b/library/cwm/src/Makefile.am
index f304218e9..802a80f90 100644
--- a/library/cwm/src/Makefile.am
+++ b/library/cwm/src/Makefile.am
@@ -15,6 +15,7 @@ ylib_DATA = \
   lib/cwm/abstract_widget.rb \
   lib/cwm/custom_widget.rb \
   lib/cwm/tabs.rb \
+  lib/cwm/tree.rb \
   lib/cwm/widget.rb