Jean Gkol makes sense because it looks like your problem probably comes down to your version of Bootstrap. I tested Bootply your code:
<button class="btn btn-default" type="button"> <span class="glyphicon glyphicon-menu-hamburger" aria-hidden="true"></span> </button>
and he worked with version 3.3.2. However, as soon as I changed the version to 3.3.1, 3.3.0 or 3.2.0, the glyphicon did not appear. Thus, it seems that the hamburger-hamburger is a completely new image in the Bootstrap Component package.
source share