$tree[0] = $arr[0];
    my @copy = @{$arr[1]};
    $tree[1] = \@copy;

   ...

   
    my ($index) = grep { $tree->[$_] eq $treeElement } 0..scalar(@$tree)-1;
    my @copy = @$subNg;
    splice @{$tree}, $index + 1, 0, \@copy;