jTree colocar imagem

class JEditionPanelTreeRenderer extends DefaultTreeCellRenderer {
    private Map<Class>&lt ? &gt, Icon&gt icons = new HashMap<Class>&lt ? &gt, Icon&gt();

    public Icon setIcon(Class&lt ? &gt aClass, Icon icon) {
        return icons.put(aClass, icon);
    }

    public Icon setIcon(Class&lt ? &gt aClass, String fileName) {
        Icon icon = new ImageIcon(getClass().getResource(fileName));

        if (fileName == null || icon == null)
            return icons.remove(aClass);

        return icons.put(aClass, icon);
    }

    @Override
    public Component getTreeCellRendererComponent(JTree tree, Object value,
            boolean sel, boolean expanded, boolean leaf, int row,
            boolean hasFocus) {
        super.getTreeCellRendererComponent(tree, value, sel, expanded, leaf, row, hasFocus);

        Icon icon = icons.get(value.getClass());

        if (icon != null)
            renderer.setIcon(icon);

        return renderer;
    }
}

Para usar a classe, faça como no exemplo abaixo:
treeRenderer = new JEditionPanelTreeRenderer();
treeRenderer.setIcon(String.class, "stringIcon.png");
treeRenderer.setIcon(Integer.class, "integerIcon.png");
treeRenderer.setIcon(Double.class, "doubleIcon.png");
suaTree.setCellRenderer(treeRenderer);