Grouping for tree with child

Please refer the example, how do I group them by year, so that their title will be shown under each year?. I am using a custom ‘myjson’ to use ‘title’ instead of value property.
http://webix.com/snippet/45e16514

http://webix.com/snippet/c2685e77

You can use .title for all rows in template, and instruct group command to create a title property for each group