You need to know *why* it has a bend!

If the whole trunk is basically straight but leaning at an angle (often because of soil washing away from the roots)(sometimes because of a damaged taproot), there is a good chance that a 3- or 4-point set of guys will hold it straight until it can make enough new roots strong enough to hold itself upright. This can take a year or two depending on how many roots were damaged when it began to lean and whether or not the soil-washing is repeated. Straighten the tree, replace the lost soil, and carefully fasten loop-top guys in place. Be sure to use sections of old garden hose to cover the guywire next to the trunk to prevent rubbing. Next summer, gradually loosen the guys and keep a close eye on the trunk to see if it begins to lean - if it does, put the guys back on for another year.

If the trunk grows straight from the ground, but then takes a bend, that is usually due to direct damage of some sort -- insects, disease, a branch torn off, line damage by a weed-whip, a chunk taken out by a passing axe, knife, or car, etc. or -harder to discern- damaged roots. There usually isn't anything that can be done about that sort of damage except watch the tree to see that it doesn't get sicker. Trees will sometimes straighten themselves above the damage as they grow, looking rather hipshot. If the tree is otherwise healthy, and the bend high enough, turn it to your advantage by using it to support or shade a birdbath or birdfeeder. OTOH, if it is still under warranty, you might prefer to discuss replacement with the nursery.