In many cases, you'll want to avoid rendering your TreeView Control with a full dataset. Rather, you'll want to load all visible nodes immediately and then retrieve data only when needed for nodes that aren't visible when the control is first loaded. This example shows you how to do that.
In the TreeView instance below, we've loaded all "top-level" nodes into the page as soon as the page loads; these nodes contain the names of several popular music groups. When a node is expanded, we use Connection Manager to access a Yahoo! Music web service that will return a list of tracks from the group that you can listen to. So when the page loads, we know nothing about our top-level nodes' children. And while the resulting TreeView instance could grow quite large through user interaction, we need only load a very light set of nodes to begin with.