Treegrid - how to mark items in a tree

I am currently using DhtmlxTreegrid, i am using a hierarchy Level1–>Level2->level3, currently
I have a requirement where i need to (mark) set a default value for only one Level2 item among all values under group Level1, the alternative here is

  1. I need to incorporate radiobuttons to level2 items, so i can select a radion button to set
    a property to any one level2 item, wish to know if radiobuttons are supported in a treegrid
    Wish to know the syntax, could not find anything specific in the document.

2 If radio buttons are not supported, i plan to use a context menu with an option called
“Set default Value” , when i right click on a level2 item and select the option–>Set default
Value , it should either highlight the row or append an image next to a level2 item denoting
that its marked as default, wish to know the syntax for appending an image to an exiting level2 item.

Request you guide me with using the approaches 1 and 2