add gtree example new file

container/gtree/gtree_z_example_avltree_test.go

@@ -0,0 +1 @@
+package gtree

container/gtree/gtree_z_example_btree_test.go

@@ -0,0 +1,7 @@
+// Copyright GoFrame Author(https://goframe.org). All Rights Reserved.
+//
+// This Source Code Form is subject to the terms of the MIT License.
+// If a copy of the MIT was not distributed with gm file,
+// You can obtain one at https://github.com/gogf/gf.
+
+package gtree_test

container/gtree/gtree_z_example_redblacktree_test.go

@@ -0,0 +1 @@
+package gtree