Refresh grouped TreeTable

I have a treetable that is grouped into a hiererchy. The user has the option to change the name of one of the parent levels. How can I refresh the data in the treetable to reflect this name change and maintain the grouping?

I have tried and failed with:

treetable.clearAll();
treetable.load(xxx.php);

Strange thing is that if I force the php file to have just 1 line in it, that line appears as 1 row in the treetable. If I try 2 manually created rows, it fails ie. blank treetable.

Hello,
Try to use updateItem.
If the grouping is server-based, in other words, the data structure arrives as a tree, so the id of the item will be known and it makes a possibility to update the item.
If the grouping is made via our method, so using id will be not so comfortable. There is better to use

let id = treetable.data.getParentId("child_item");
treetable.updateItem(id, { name:"New name" });

Strange thing is that if I force the php file to have just 1 line in it, that line appears as 1 row in the treetable. If I try 2 manually created rows, it fails ie. blank treetable.

Could you please send a sample where I can see what exact arrives from the server? Or is better will be to see a snippet of the code