diff --git a/ptml/ptml.g4 b/ptml/ptml.g4
index 38a66cf..6e1b833 100644
--- a/ptml/ptml.g4
+++ b/ptml/ptml.g4
@@ -1,6 +1,6 @@
 grammar ptml;
 
-tree    : internal_node Names+ | internal_node+ Names+
+tree    : internal_node Names+ | internal_node (Names|tree)+
         ;
 internal_node : 'sequence' | 'selector' | 'parallel' | 'decorator';
 Names : [a-zA-Z_][a-zA-Z_0-9]* ;
\ No newline at end of file