It sounds like you may be looking for a basic tutorial on the definition of a tree structure. If that is so, I recommend having a look at Wikipedia (tree structures) which I'm finding has good introductions to basic computer science concepts such as this these days..

As an aside, I think Perl lends itself quite naturally to tree structures. Having references makes building trees very simple. For example, consider a table of contents:

  my %contents = (
    1 => [ 'Introduction', undef ],
    2 => [ 'Design', {
        1 => [ 'Wheels', undef ],
        2 => [ 'Frame', undef ],
        3 => [ 'Electronics', {
            1 => [ 'Dashboard', undef ],
            2 => [ 'Fuel Injection', undef ],
        },
        4 => [ 'Petrol Tank', undef ],
    },
    3 => [ 'Summary', undef ],
  );
[download]

Merely defining things these ways is, by definition, a tree. If references are tripping you up, then read about pointers.. and re-read until you become more comfortable with this concept.