Hi,
It looks like there may be an error on this page:
https://docs.dhtmlx.com/api__link__dhtmlxtreeview_loadstruct.html
it says
myComponent.loadStruct({data:[{id:"a1",..},{id:"a2",..}]});
when in fact that does not work, it needs to be:
myComponent.loadStruct([{id:"a1",..},{id:"a2",..}]);
I have seen this same problem on another component too but I can’t remember which one.