docs: static LeafNodeDupMutable convert(@NotNull ILeafNode ln, @NotNull BTreeMutable mainTree) {
  
          final boolean isLeafNodeDup = ln.isDup();
          if (isLeafNodeDup && ln instanceof LeafNodeDupMutable) {
              return (LeafNodeDupMutable) ln;
          }
  
          // wrapper tree that doesn't allow duplicates
          final BTreeDupMutable dupTree = isLeafNodeDup ?
                  ((LeafNodeDup) ln).getTreeCopyMutable() :
                  new BTreeDupMutable(
                          new BTreeEmpty(mainTree.getLog(), mainTree.getBalancePolicy(), false, mainTree.getStructureId()),
                          ln.getKey()
                  );
          dupTree.mainTree = mainTree;
          return convert(ln, mainTree, dupTree);
      }