sap.m.Tree How to update view of the tree with custom code only once?

Question

I am trying to get rid of the arrow icons on my lowest tree leaf items... I tried to do it in the "onUpdateFinished" event of the tree, however, it seems this event triggers every time something changes, e.g user expands a node etc. Is there a binding finished event for the component maybe?

Furthermore, I try to set the icon to null if the level of items is 1:

sOTree.getItems().map(item => {
                    if (item.getLevel() === 1) {
                        item.ExpandedIconURL = null;
                        item.CollapsedIconURL = null;
                    }
                });

However, this seems to happen only when I expand a node, after that, the icon dissapears but why?