You might be able to use that handle to make a Win32::GUI::TreeView object like this

use Win32::GUI;
my $tree = bless( {
      '-type' => 0,
      '-name' => 'Guessing',
      '-handle' => $treehandle,
      '-accel' => 0
    }, 'Win32::GUI::TreeView' )
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then maybe you can set/change data easier