The two options to have a nested grid are with a dialog or as dropdown when the main grid is in tree mode.

To see them, please visit the following demo: https://codepen.io/svetoslavjqwidgets/pen/OJBpMVX

When you load it initially, you will see on the left side arrows on each row. Clicking the arrow will expand the row detail with the nested grid.
To make it dialog, uncomment this code in the rowDetails object:
// dialog: {
// enabled: true
// }

I hope this helps!

Best Regards,
Svetoslav Borislavov

Smart UI Team