You don't have to use Magic Lantern (ML) to use bulb mode with your Canon EOS Rebel T2i. There is an advantage to using ML which allows you to take bracketed shots without cycling the mirror between each shot. It may also allow you to take multiple images in burst mode (all at the same exposure level) without cycling the mirror.

To get into Bulb mode with the T2i, set the camera to Manual (M) mode and adjust the shutter speed (Tv) to Bulb. It is one click past 30 sec. (See page 83-84 of your T2i Instruction Manual)

If you are going to take multiple exposures and stack them as many do when creating star trails, you want to turn Long Exposure Noise Reduction (LENR) off. It is set under Custom Function menu II: Image. C.Fn-4 needs to be set to "0" (off). If LENR is set to "on" or "Auto", there will be a gap between each exposure while a dark frame is taken with the shutter closed. This is a very useful feature for single exposures when doing astronomical photography, but gets in the way when needing to do continuous multiple exposures. (See page 193 of your T2i Instruction Manual)