I mean it uses :
QTreeView::branch:has-siblings:!adjoins-item
{
border-image: url(StyleSheets/Default/branch-vline.png);
}

QTreeView::branch:has-siblings:adjoins-item
{
border-image: url(StyleSheets/Default/branch-more.png);
}

QTreeView::branch:!has-children:!has-siblings:adjoins-item
{
border-image: url(StyleSheets/Default/branch-end.png);
}
But that use this stylesheet only when I close a parent and reopen it with all item opened, before doing this action, it has arrow on the left of each item.
One thing weird too is that replace an item with no children by the good stylesheet image but before doing the action, one arrow is on the left of the item.
Here a screenshot before and after doing this action. I would only use the stylesheet if possible.

Step1 : I open a folder
http://uppix.com/f-Step153906b180016a77f.png

Step2 : I open each folder, they have no children
http://uppix.com/f-Step253906b690016a781.png

Step3 : I close the parent folder and reopen it
http://uppix.com/f-Step353906b890016a782.png