Setting Icon of Jtree on expanding

Question

following multiple tutorials and question like this or this I am trying to create a Jtree dom which should be able to have different Icons depending on the properties beeing set in the application, but i am not able to find a way to set the icon properly since it doesn´t display correct after beeing set.

I did create my own class XML_JTRE_ELEM which has JTree as super class and also implements the TreeExpansionListener

The overwritten Method for the expansion looks like this

public void treeExpanded(TreeExpansionEvent event) {
    TreePath path = event.getPath();
    DefaultMutableTreeNode node = (DefaultMutableTreeNode) path.getLastPathComponent();
    XML_JTREE_ELEM elem = (XML_JTREE_ELEM)node.getUserObject(); // Get the current JTREE
    for(String key : elem.getSubTrees().keySet()) {
        // Set the icon dynamcally for each subtree item
        elem.getSubTrees().get(key).setIcon();
    }
}

the setIcon Method simply sets a new CellRenderer for each subtree

public void setIcon() {
    DefaultTreeCellRenderer renderer = new TagRenderer(ImageList.sum);
    this.setCellRenderer(renderer);
}

The CellRenderer itself looks like this:

private class TagRenderer extends DefaultTreeCellRenderer{
    private static final long serialVersionUID = 1L;

    private ImageIcon _icon;

    public TagRenderer(ImageIcon icon) {
        this._icon = icon;
    }

    @Override
    public Component getTreeCellRendererComponent(JTree tree,
            Object value, boolean selected, boolean expanded,
            boolean isLeaf, int row, boolean focused) {
        setIcon(_icon);
        System.out.Println(_icon.toString());
        return this;
    }
}

When i am printing out the _icon i am getting the expected result file:/C:/java_ws/project/bin/resources/Sum.png

The output i am getting looks like the following:

but according to the debug messages it is setting the icons for each JTree element below the Test Jtree properly . Do i need to reload the model of the JTree after setting the icon, or is the approach of setting the icon this way wrong in general?