use strict;
use warnings;
use Data::Dumper;

use Data::Diver qw( DiveRef );

my $data = {};

while (<DATA>) {
   chomp;
   my @keys = split /:/;
   my $val = pop(@keys);
   my $ref = DiveRef( $data, map \$_, @keys );
   push @$$ref, $val;
}

print Dumper($data);

__DATA__
gkey01:key1:1 2 3 4 5 6 7 8
gkey02:key1:key2:key3:1 2 3 4
gkey03:key1:key2:key3:key4:1 2 3 4 5 6 7 8
gkey04:key1:key2:key3:1 2
gkey05:key1:key2:key3:key4:1 2
gkey06:key1:key2:key3:key4:key5:1 2 3
gkey07:key1:key2:1 2 3 4 5 6 7 8 9
gkey08:key1:key2:key3:key4:1 2 3 4 5 6 7
gkey09:key1:1 2 3 4 5 6 7
gkey10:key1:1 2 3 4 5 6
gkey11:key1:1 2 3 4
gkey12:key1:key2:1 2 3 4 5 6 7 8 9 10
gkey13:key1:key2:key3:key4:1 2 3 4
gkey14:key1:key2:key3:1 2
gkey15:key1:1 2 3 4 5 6 7
gkey16:key1:key2:1
gkey17:key1:key2:key3:1 2 3 4 5 6 7 8 9 10
gkey18:key1:key2:1 2 3 4 5 6 7
gkey19:key1:key2:key3:1 2 3 4 5 6 7 8
gkey20:key1:key2:1 2 3 4 5 6 7 8 9

##</code><code>##

$VAR1 = {
          'gkey17' => {
                        'key1' => {
                                    'key2' => {
                                                'key3' => [
                                                            '1 2 3 4 5 6 7 8 9 10'
                                                          ]
                                              }
                                  }
                      },
          'gkey11' => {
                        'key1' => [
                                    '1 2 3 4'
                                  ]
                      },
          'gkey01' => {
                        'key1' => [
                                    '1 2 3 4 5 6 7 8'
                                  ]
                      },
          'gkey20' => {
                        'key1' => {
                                    'key2' => [
                                                '1 2 3 4 5 6 7 8 9'
                                              ]
                                  }
                      },
          'gkey07' => {
                        'key1' => {
                                    'key2' => [
                                                '1 2 3 4 5 6 7 8 9'
                                              ]
                                  }
                      },
          'gkey06' => {
                        'key1' => {
                                    'key2' => {
                                                'key3' => {
                                                            'key4' => {
                                                                        'key5' => [
                                                                                    '1 2 3'
                                                                                  ]
                                                                      }
                                                          }
                                              }
                                  }
                      },
          'gkey19' => {
                        'key1' => {
                                    'key2' => {
                                                'key3' => [
                                                            '1 2 3 4 5 6 7 8'
                                                          ]
                                              }
                                  }
                      },
          'gkey16' => {
                        'key1' => {
                                    'key2' => [
                                                '1'
                                              ]
                                  }
                      },
          'gkey10' => {
                        'key1' => [
                                    '1 2 3 4 5 6'
                                  ]
                      },
          'gkey18' => {
                        'key1' => {
                                    'key2' => [
                                                '1 2 3 4 5 6 7'
                                              ]
                                  }
                      },
          'gkey04' => {
                        'key1' => {
                                    'key2' => {
                                                'key3' => [
                                                            '1 2'
                                                          ]
                                              }
                                  }
                      },
          'gkey03' => {
                        'key1' => {
                                    'key2' => {
                                                'key3' => {
                                                            'key4' => [
                                                                        '1 2 3 4 5 6 7 8'
                                                                      ]
                                                          }
                                              }
                                  }
                      },
          'gkey05' => {
                        'key1' => {
                                    'key2' => {
                                                'key3' => {
                                                            'key4' => [
                                                                        '1 2'
                                                                      ]
                                                          }
                                              }
                                  }
                      },
          'gkey08' => {
                        'key1' => {
                                    'key2' => {
                                                'key3' => {
                                                            'key4' => [
                                                                        '1 2 3 4 5 6 7'
                                                                      ]
                                                          }
                                              }
                                  }
                      },
          'gkey12' => {
                        'key1' => {
                                    'key2' => [
                                                '1 2 3 4 5 6 7 8 9 10'
                                              ]
                                  }
                      },
          'gkey14' => {
                        'key1' => {
                                    'key2' => {
                                                'key3' => [
                                                            '1 2'
                                                          ]
                                              }
                                  }
                      },
          'gkey13' => {
                        'key1' => {
                                    'key2' => {
                                                'key3' => {
                                                            'key4' => [
                                                                        '1 2 3 4'
                                                                      ]
                                                          }
                                              }
                                  }
                      },
          'gkey15' => {
                        'key1' => [
                                    '1 2 3 4 5 6 7'
                                  ]
                      },
          'gkey09' => {
                        'key1' => [
                                    '1 2 3 4 5 6 7'
                                  ]
                      },
          'gkey02' => {
                        'key1' => {
                                    'key2' => {
                                                'key3' => [
                                                            '1 2 3 4'
                                                          ]
                                              }
                                  }
                      }
        };