[Plugin: WP-dTree] Space before 3rd level links

I think 3rd level links have a too large indent. I was looking what’s generating the indent and it’s the (transparent) “empty.gif” and for the 3rd level there seems to be three of them instead of two. I noticed this while swapping the transparent “empty.gif” with a solid one.
Is there a quick fix to get the plugin to only generate two “empty.gif” on 3rd level links?

In future versions it would be nice to choose the size of the indent.