Hello,

I have been looking into your question and what I could say is that depending on your requirement you could re-template the IgxTreeGrid column headers or its toolbar and place a custom button inside the template.

In case you require to have such a button inside the grid's toolbar, a topic that you might consider useful could be found here.

If the button should be inside some column header an approach I could suggest is using the igxHeader directive as it is demonstrated in this topic.

In both scenarios when the button is clicked you could call the tree grid expandAll or collapseAll method in order t achieve the described behavior.

In addition, a small sample with a custom button inside the grid's toolbar that expands/collapses all rows could be found here.

Please do not hesitate to contact me if you need any further assistance with this matter.  

Sincerely,
Teodosia Hristodorova
Software Developer
Infragistics