diff -r adcaaf6c9910 -r ff20b44b2fc8 src/HOL/Library/Tree.thy
--- a/src/HOL/Library/Tree.thy	Wed Jan 13 00:12:43 2016 +0100
+++ b/src/HOL/Library/Tree.thy	Wed Jan 13 09:38:16 2016 +0100
@@ -7,8 +7,8 @@
 begin
 
 datatype 'a tree =
-  Leaf ("\<langle>\<rangle>") |
-  Node (left: "'a tree") (val: 'a) (right: "'a tree") ("\<langle>_, _, _\<rangle>")
+  is_Leaf: Leaf ("\<langle>\<rangle>") |
+  Node (left: "'a tree") (val: 'a) (right: "'a tree") ("(1\<langle>_,/ _,/ _\<rangle>)")
   where
     "left Leaf = Leaf"
   | "right Leaf = Leaf"