tentative performance optimization (needs benchmarks)

Author: gp-lnuff

src/SelectTree.php

@@ -246,7 +246,10 @@ private function buildTreeFromResults($results, $parent = null): Collection
         );
 
         // Move any remaining children from the cache into the root of the tree, since their parents do not show up in the result set
-        $resultMap[$parent] = array_merge(...array_values($orphanedResults));
+        $resultMap[$parent] = [];
+        foreach($orphanedResults as $orphanedResult){
+            $resultMap[$parent] += $orphanedResult;
+        }
 
         // Recursively build the tree starting from the root (null parent)
         $rootResults = $resultMap[$parent] ?? [];