Normally, the UI paradigm of all tree views assumes that the user selects on node at a time. It looks very natural and clear, and multiple selection mode would be confusing. So, my advise would be not trying to create such tree view style.
However, if you really want something like that, you can find some solution. First of all, people usually use checking instead of selection. For example, see this:
http://stackoverflow.com/questions/7158876/multiple-selection-tree-view-control-for-asp-net-web-application-using-c-net[
^].
Moreover, as this is a Web application; and tree view is not a native HTML element; instead, ASP.NET generates a tree view based on other HTML elements. So, you can create a different tree view class to develop a very different tree view style; or you can customize available tree view. Please see these CodeProject articles:
C# TreeView with multiple selection[
^],
Multi-Select TreeView Control in C#[
^].
If you want, you can probably find some more:
http://bit.ly/xbvqur[
^].
—SA
Submit an article or tip