You can have a bold font on a TreeGrid. Create your own renderer and enhance the HTML returning by the renderer.

private class BoldGridCellRenderer extends TreeGridCellRenderer<ModelData> {
	protected String getText(TreeGrid<ModelData> grid, ModelData model, String property, int rowIndex, int colIndex) {
		return "<span style=\"font-weight:bold\">" + super.getText(grid, model, property, rowIndex, colIndex) + "</span>";
	}
}

Add the renderer to your tree column (use always TreeGridCellRenderer for that column!).

ColumnConfig name = new ColumnConfig("name", "Name", 300);
name.setRenderer(new BoldGridCellRenderer());