When calling TreeItem.setValue(), the TreeCell will be updated (see com.sun.javafx.scene.control.skin.TreeViewSkin#rootListener) This is not the case when calling TreeItem.setGraphic().

UseCase: I've got an expensive icon loading process which loads the icons for the TreeItems in the background. Current workaround:

treeItem.setGraphic(new ImageView(image));
Event.fireEvent(treeItem, new TreeItem.TreeModificationEvent<>(TreeItem.valueChangedEvent(), treeItem, treeItem.getValue()))