Hi Roger,
To achieve the desired appearance I would suggest you to add a click event handler to the arrow button. When the arrow is clicked and the popup for filtering appears, you could find all the checkboxes through the
'.k-checkbox' class. Then for each checkbox, if it is checked, you could hide the respective item. Note, that you will need to exclude the checkbox corresponding to the 'All' node (marked in orange below). In order to ensure, that the checkboxes are rendered by the time you are trying to check their values, you will need to use
setTimeout function.
Here you will find a Dojo example, where the approach described above is implemented.
I hope this helps.
Regards,
Neli
Progress Telerik