You can "brake" bedrock with a tree, dark oak.
As described in this redit thread http://www.reddit.com/r/Minecraft/comments/1qdmqm/how_to_break_bedrock_in_vanilla_survival_172/

To replicate, get on top of the nether or to the bottom of the world.
have some dark oak sapplings and bonemeal.
Build a 2x2 dirt platform. Use bonemeal on the saplings to make the tree grow and then knock out the blocks where the sapling were and replant use bonemeal to make it grow and sometimes it grows from top down. Then you can remove the logs as they have replaced the bedrock.

http://www.youtube.com/watch?v=wCjmc0lKfsE and http://www.youtube.com/watch?v=2ABwAf8iMRw

p.s. dis not find any dups, using search bedrock or tree or brake bedrock