DXTreeList - How to implement summary footers

At the moment, our TreeListView does not provide the capability to show summary footers for its groups. This example demonstrates how to implement this functionality manually by using a custom DataRowTemplate.

This workaround has a few limitations:
1. It supports only a two-level structure.
2. The context menu for summary footers is not supported.
3. The grid's horizontal scrolling is not supported.