Is there a simple solution to this?

Yes -- as long as your format doesn't have any more complexity that you haven't told us about yet.

There's a general approach to tree-building that's applicable here: Keep a stack of your "active" container, and every time you find a line with a "{" on the end of it, push a new container on to the stack. On lines with a "}", pop the active item off the stack. Every other piece of data that we find can get pushed into whichever container is currently active.

Of course, if your format includes escape characters, multi-line elements, or other complications, you may need to use one of the industrial-strength parser-generators... But for a simple format, we can roll our own.

Take a look at the output of the below, with and without $fewer_indents set true, and modify as desired.

sub parse_brackets {
  my @parse;
  my @stack = \@parse;
  
  my $fewer_indents = 1;   # Try setting this to 0 or 1
  
  my $line_no;
  foreach my $line ( @_ ) {
    $line_no ++;
    $line =~ s/\A\s+//;
    $line =~ s/\s+\Z//;
    if ( $line !~ /\S/ ) {
      next;
    } elsif ( $line =~ s/\s*\{$// ) {
      my @line = split ' ', $line;
      push @{ $stack[0] }, \@line;
      if ( $fewer_indents ) {
    unshift @stack, \@line;
      } else {
    my @kids = ();
    push @line, \@kids;
    unshift @stack, \@kids;
      }
    } elsif ( $line eq '}' ) {
      shift @stack; 
      scalar @stack or die("Too many right brackets at line $line_no")
+;
    } else {
      push @{ $stack[0] }, $line;
    }
  }

  return @parse;
}

use Data::Dumper;

print Dumper( parse_brackets( split "\n", <<'EXAMPLE' )  );

  page p1 {
      question 4B {
      label {
          Do you like your pie with ice cream?
      }

      single {
          1 Yes
          2 No
      }
      }

      question 4C {
      label {
          Do you like your pie with whipped cream?
      }

      single {
          1 Yes
          2 No
      }
      }
  }

EXAMPLE
[download]