Also a tree in a old 3d game
Reference
An interactive explanation of quadtrees - 2014
Terrain Tile Picking - 2013
Quick Tip: Use Quadtrees to Detect Likely Collisions in 2D Space - 2012
Spatial indexing with Quadtrees and Hilbert Curves - 2009
Quadtrees - 2001
Quadtree and Octree Culling Alternative - 2001
Tutorial 5: Quad Trees