Strange leaf image in my Treeview

[Romu]

Hi all,
I'm pretty newbie in ASP.Net, I've started to create a web page which
contains a Treeview. And for all not expandable elements (the leaves of the
tree), a black frame is displayed around the image area whatever the image
set is.

Any idea how to remove this?

Another question is: is there a way to set the NoExpandImageUrl per leaf and
not for the whole Treeview?

Thanks in advance.