No configuration available to define headers for child in Advanced Tree Grid in Thingworx

Recently I have been working with the advanced tree grid in Thingworx 8.5 and I had to put headers for the childs which were not as per the parent headers. Could not find any option to do so. 

I tries configuration as JSON using Service also but did not find any Key to configure child columns.

I would really appriciate any help on this.

Thanks !!