That long bar under your bike seat that gives you the support you need is called a seat post, and it is a rather necessary part of your mountain bike or road bike. Now, there are a number of seat posts on the market for any type of bike you can think of including BMX bikes and racing bikes.
Seatposts come in a variety of styles, colors and made from different materials. Perhaps your seat post is too short and a longer one will give you the height your desire, or maybe you had an accident and bent you seat post and need to have it replaced. Regardless the reason, you can bet we have the seat post you are looking for, even if you ride with a banana seat.