Quick and dirty. (Well, dirty anyway.)

>perl -wMstrict -le
"use Data::Dumper;
 ;;
 my @lines = qw(a/b/c/d/e  a/b/c/f  a/g  x/y);
 my %hash;
 for my $line (@lines) {
   eval qq{\$hash{ @{[ join '}{', split qr{/}xms, $line ]} } = 1;};
   }
 print Dumper \%hash;
"
$VAR1 = {
          'a' => {
                   'g' => 1,
                   'b' => {
                            'c' => {
                                     'd' => {
                                              'e' => 1
                                            },
                                     'f' => 1
                                   }
                          }
                 },
          'x' => {
                   'y' => 1
                 }
        };
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