Flex Tree leaf-element highlighting while drag&drop

i have TileList from which i'm dragging开发者_StackOverflow中文版 some stuff(image) to Tree (something like dragging sounds into playlist in iTunes), but when i can drop this stuff, i see only underline, this mean i can drop it only under or above some leaf-element in that Tree. How can i force it to hide this black underline and highlight leaf-element to which i wanna drop my stuff.

Thanks

The last example on this page has pretty much exactly what you're looking for. http://www.adobe.com/devnet/flex/quickstart/working_with_tree/