scenic cement
It's not scenic, and, for trees, it's more like cement(heavy) than adhesive for leaves.
I would recommend the prescribed preservation technique from the "manufacturer / distributor".
I would recommend clear gloss spray (rattle can from Ace hardware, or equivalent it's less expensive than the testor's, to use as the adhesive for attaching leaves.)
I would recommend using Woodland Scenics "coarse turf", sifted, with a small flour sifter so only the smaller bits go on the tree. The larger remains can be used for ground cover. It usually takes three to four applications. For S, or O scale, you can use the coarse turf as is, but sprinkled from about 18" above.
Tapping the tree will help the "leaves" drop into the interior areas.( the unused material can be recycled, if you have a "ground cloth", or newspaper, under the trees to catch the extras. ) I usually start with one application with the tree inverted, and finish with the tree upright.
If the trees will not be subjected to handling / moving / physical contact, you can get by with spray paint for color, then clear to attach the leaves.
For larger trees, use some other form of armature, and attach the supertree pieces to it.
The small branch pieces can be used to make bushes. Cut 1/8" styrene tube in 3/16"-1/4" lengths. Insert from two, to as many as will fit, branches in each tube piece, and set with glue. Apply leaves as per above, and set aside.
The bushes can be planted by making a 1/8" dia. hole in the scenery base, and plugging the "tubes" in.