code: private function populateCompressedSnapWithPv($tree, $compressionData, $keyPv)
      {
          $result = $tree;
          foreach ($compressionData as $custId => $data) {
              /* 0 - PV, 1 - parentId */
              $pv = $data[0];
              $entry = $result[$custId];
              if (is_array($entry)) {
                  $entry[$keyPv] = $pv;
              } else {
                  $entry->set($keyPv, $pv);
              }
              $result[$custId] = $entry;
          }
          return $result;
      }
docs: Populate phase 1 compressed $tree with compressed PV data.
  
  @param array $tree compressed tree w/o PV data
  @param array $compressionData compression data with compressed PV
  @return array compressed tree with PV data