I found the following:

If you set the ExpandDepth = 0 all nodes are collapsed at startup, but then for every click all nodes are collapsed again. Which is better than to have the entire tree expanded on every click. (I added a sitemappath at the top of the page to show where exactly you are in the treeview). Secondly, to be able to expand a node when you click on the description added the following code:

protected void tvMenuNode_DataBound(Object sender, TreeNodeEventArgs e)
if (e.Node.NavigateUrl == "")
{
e.Node.SelectAction = TreeNodeSelectAction.Expand;
}

}

I still need to find a way to keep the selected node expanded.

you may try :::

treeid.CollapseAll();