#!/usr/bin/perl

use strict;


my %found = ( start => ["a", "b", "d", "g"],
              a => ["c","e"],
              b => [],
              c => ["f"],
              d => ["e"],
              e => [],
              f => [],
              g => [],
             );

print_tree('start', '');

sub print_tree{
    my ($sub, $tab) = @_;
        foreach (@{$found{$sub}}){
                 print "$tab$found{$sub}[$_]\n";
                 $tab .= "\t";
                 print_tree($found{$sub}[$_], $tab);
                 }
        }