Single cell style of treetable parent row

Is it possible to display the parent row in a treetable as one cell (combined table cells?), so the parent text continues for the width of the table? Thus, leaving the children to display as normal table data in multiple columns as designed. In essence, I’d like the parent rows to be a ‘tree’ style component, and the child rows to be the ‘table’ component. I have not found a css way to do this, and am wondering if it can be done. (Vaadin 7.3.9)

Any suggestions?