Babe Ruth rules allows USA Baseball (aka Little League bats) or BBCOR bats.  BBCOR is also the high school standard bat.
Wooden bats must be one piece (cannot be 2 or more put together) and since they must be one piece, bamboo is not allowed. Bamboo bats, by definition, are many pieces of bamboo put together.  Bamboo is not wood, it is a grass.

In short- All non-wood bats must either be USA Baseball stamped, or BBCOR Stamped.  USSSA is not USA, and USSSA (also known as "U-Trip" are not legal.

Confused?  Below is an illustration of the various bat stamps- note there are only two permitted in Babe Ruth play.