Here's the new scenery and wood glue from Scenic Express. It's from Europe and combines the best features of white glue and liquid latex.
It's made for most scenery applications and is water soluble. Hal Reynolds of Atlantic Scale Models has been experimenting with it.
He says you can dilute this with water and dip the Scenic Express SuperTrees in it. You need several dipping and drying cycles to make them flexible while keeping that fine branch structure. I need to buy some to try it out!