Since I've never ever heard of a wisteria tree, I'm going to go with vine here.

They are vines by nature and are usually grown as such but with support, training and regular pruning can be made into a tree shape.

Regardless of whether you grow this plant in its natural vining form or trained as a small "tree", it will need support. And a pretty heft support system as well!! In time, the trunk of the vine can get very woody and large and if allowed to grow unimpeded, it twists around the support system, applying considerable torquing force. I have seen a wisteria rip out metal pipes (like the types that used to be used for outdoor clotheslines) and dislodge 4"x4" deck supports. This is not a vine for a wimpy little trellis!!

And before planting, do a search for Wisteria on GardenWeb. It can be a fair amount of work (pruning, removal of suckers and seedlings, etc.) to keep it looking good.

For me at least, the native wisteria (dunno if we're talking about the Asian imports or the native), is very restrained and I *wish* it would grow faster.