docs fix

examples/docs/en-US/tree.md

@@ -250,7 +250,7 @@ Only one node among the same level can be expanded at one time.
 
 ::: demo
 ```html
-<el-tree :data="data" :props="defaultProps" @node-click="handleNodeClick"></el-tree>
+<el-tree :data="data" :props="defaultProps" accordion @node-click="handleNodeClick"></el-tree>
 
 <script>
   export default {

examples/docs/zh-CN/tree.md

@@ -262,7 +262,7 @@
 
 ::: demo
 ```html
-<el-tree :data="data" :props="defaultProps" @node-click="handleNodeClick"></el-tree>
+<el-tree :data="data" :props="defaultProps" accordion @node-click="handleNodeClick"></el-tree>
 
 <script>
   export default {