Thanks a lot for the great info ! I had never heard of the "burning bush" variety before but the name makes sens ! There is practically no information regarding this variety online. I found only a faulty stamp with this variety sold by Maresch in 2007 for 90$.
I looked online for the book you mention but it seems to be out of stock everywhere. I also saw this book that seems very interesting :
The Five Cent Beaver II. Plating the More Notable Varieties and Re-entries, 2007 by Kenneth A. Kershaw
but the book is 200$.
Being a hunter for re-entries and varieties, I use
www.re-entries.com very often. This stamp is not on the site. I will email concerning the possible re-entry on this one although I had emailed Mr.Trimble a month ago and never got a reply.