Hi,

There is no easy way to have SlideMenu to fill the spliter panel. Options you can consider are:

1. Use the "Single Expand" feature of the TreeView control instead of a SlideMenu. See here for a working example:

http://demo.essentialobjects.com/Demos/TreeView/Features/Single%20Expand/Demo.aspx

The difference between a "Single Expand" TreeView and the SlideMenu is the "sliding pane" does not take a fixed height. Other than that, you will be able to customize the TreeView's style to make it look exactly like a slide menu

When you use a TreeView, you may also want to set AutoScroll to false since the splitter pane already automatically have scroll bars;

2. Set the splitter pane's background as the same color as the TreeView/SlideMenu's background. This makes it look like that the TreeView/SlideMenu filled the whole splitter pane even though it actually does not;

Hope this helps. Please feel free to let us know if you have any questions.

Thanks!