# using a longer perl script:

$ ls | head -11 | perl -pe '$_="" if($.==1);s{$/}{ } unless($.%2)'
Documents Downloads
Library Movies
Music Pictures
Public Sites
bin cgi-bin

# using a longer command line:

$ ls | head -11 | tail +2 | perl -pe 's{$/}{ } if($.%2)'
Documents Downloads
Library Movies
Music Pictures
Public Sites
bin cgi-bin