function transcodeSubtreeTiles(content, subtree, placeholderTile, childIndex) {
  const rootBitIndex = 0;
  const rootParentIsPlaceholder = true;
  const rootTile = deriveChildTile(
    content,
    subtree,
    placeholderTile,
    childIndex,
    rootBitIndex,
    rootParentIsPlaceholder,
  );

  const statistics = content._tileset.statistics;

  // Sliding window over the levels of the tree.
  // Each row is branchingFactor * length of previous row
  // Tiles within a row are ordered by Morton index.
  let parentRow = [rootTile];
  let currentRow = [];

  const implicitTileset = content._implicitTileset;
  for (let level = 1; level < implicitTileset.subtreeLevels; level++) {
    const levelOffset = subtree.getLevelOffset(level);
    const numberOfChildren = implicitTileset.branchingFactor * parentRow.length;
    for (
      let childMortonIndex = 0;
      childMortonIndex < numberOfChildren;
      childMortonIndex++
    ) {
      const childBitIndex = levelOffset + childMortonIndex;

      if (!subtree.tileIsAvailableAtIndex(childBitIndex)) {
        currentRow.push(undefined);
        continue;
      }

      const parentMortonIndex = subtree.getParentMortonIndex(childMortonIndex);
      const parentTile = parentRow[parentMortonIndex];
      const childChildIndex =
        childMortonIndex % implicitTileset.branchingFactor;
      const childTile = deriveChildTile(
        content,
        subtree,
        parentTile,
        childChildIndex,
        childBitIndex,
      );
      parentTile.children.push(childTile);
      statistics.numberOfTilesTotal++;
      currentRow.push(childTile);
    }

    parentRow = currentRow;
    currentRow = [];
  }

  return {
    rootTile: rootTile,
    // At the end of the last loop, bottomRow was moved to parentRow
    bottomRow: parentRow,
  };
}
Transcode the implicitly-defined tiles within this subtree and generate
explicit {@link Cesium3DTile} objects. This function only transcode tiles,
child subtrees are handled separately.

@param {Implicit3DTileContent} content The implicit content
@param {ImplicitSubtree} subtree The subtree to get availability information
@param {Cesium3DTile} placeholderTile The placeholder tile, used for constructing the subtree root tile
@param {number} childIndex The Morton index of the root tile relative to parentOfRootTile
@returns {TranscodedSubtree} The newly created subtree of tiles
@private