I didn't see an option to have 2 talent trees at my class trainer. Is this feature available for Death Knights?
Yes, all classes can learn dual talent specialization at level 30. However it first must be purchased from your trainer for 30g.
Simply return to Acherus, the Ebon Hold and talk to any of the trainers that would normally teach you new abilities. One of the speech options with the trainer should be "Learn About Dual Talent Specialization". Once you have done this, there should now be an extra tab on the right hand side of your talent trees to switch between the two talent specs.
You may need to have completed the Death Knight quest line to unlock this option. E.g. be level 58.
Image source: Joystiq.com
It is available for all classes, so yes your Death Knight can also have it