Yes this is possible. Any menu type created in the theme.skin with
portal:FlexMenu as its tag can be used to display all pages/levels, and you can style it to look however you'd like. The primary settings that cause the menu to show all pages/levels are
MaxDataRenderDepth="-1" - these options allow you to control the starting node for the menu and the depth it will go to underneath that node, but when given a value of "-1" they both will show all pages/levels.