How does the Spatial data structures work?

Hi, i’m new to cesium and confused about the “Spatial data structures”. There are two questions for me.
First, where does this concept show? Does it is reflected in “tileset.json” and its “children”?
Second, How do we implement this? For example, when we convert citygml data to 3d tiles, should we use “Quadtree” to divide the whole data into different childrens and then convert following the specification? Or just convert the whole data into 3d tiles then using “Quadtree” to divide the 3d tiles into different childrens?
Thanks for your reply!