What's this tree?

Looks like Wisteria.

 

Piggy30 is right that's Wisteria, messy messy messy.

 

Wisteria is right. It's gorgeous but vining & vigorous (at least in northern California) & can be trained almost like a grape vine. Comes commonly in white and purple. Problem is that it's easily trained against walls, trellises, etc. but quickly outgrows its mounts & supports. I know people that have had decks pulled apart by wisteria run amuk. Caution advised ...

 

That's probably chinese wisteria, trained into a tree form. That type is the one that goes rampant and tears things down. I've always wanted to set up a battle of wisteria vs. kudzu. Maybe plant each at the base of a telephone poll and film the war in slo motion. That would be freakin' awesome....

But i digress. I meant to say that there is an american (native) wisteria that might grow in Denver that is supposed to be MUCH better behaved and I think flowers more readily. You might look into that.

 

There's a humongazoid wistaria tree in San Gabriel, it covers city blocks, I'm told....
linkage:
http://www.sierramadrenews.net/wistaria.htm

 

I have this and I suspect it's the native species but I don't really know. It ate a persimmon tree and is now eating a pine. It will be cut back hard soon since the flowers are gone here.

 

Our neighbors behind us had a gorgeous, purple wisteria that was on an arbor and draped into our back yard. I miss it so:< It devoured the arbor in about 8 years and it literally fell into pieces. So the neighbors removed the arbor and the wisteria. Sniff. I say go for it. Just don't build anything too expensive for it to crawl over or keep it cut back.