This sample demonstrates the Tree Grid header template feature. In this sample, we have shown custom icons in the column headers.
The Tree Grid provides a way to define a custom element in header
element. columns->headertemplate property accepts
either string or HTML element`s ID value, which will be used as the
template for the header cell.
{" "} In this demo, we have render customized template for all column headers.
More information about Header template can be found in documentation section.