I see what you mean. Maintaining two separate downloads (which also means to have two separate DLLs) would be too costly for us thus it's not practical. If you already have a license for an old version of TreeView, you maybe able to get a new license for free if you are still within the free upgrade period:
http://www.essentialobjects.com/Forum/Default.aspx?g=posts&t=8If your free upgrade period has already expired, then you would need to place an upgrade order order to upgrade to the new version. Otherwise you will not be able to use the new progress bar and your old TreeView at the same time.