Ok select tree, edit it, as you woudl any object (bottom righthand corner of screen, object list, select item, right click, edit) :)

now hit the x2 button, to double polygon count ;)

another thing you can do is import trees from XFROG or the like which are super high quality and nice for close ups, but, unliek Vue's native plants, won't always be different
XFOG plants are meshes so never change, thus not so good for large numbers of plants, which is where Vue plants really shine.
XFROG has a few freebie plants on their site, which is very handy :D

"I'd rather be a Fool who believes in Dragons, Than a King who believes in Nothing!" www.silverblades-suitcase.com
Free tutorials, Vue & Bryce materials, Bryce Skies, models, D&D items, stories.
Tutorials on Poser imports to Vue/Bryce, Postwork, Vue rendering/lighting, etc etc!