Recursively decompose the underlying space into four equal area blocks as long as a block contains more than bucket capacity of rectangles. For more details, see pages 481-483 of Samet, Foundations of Multidimensional and Metric Data Structures or, see Samet, Design and Analysis of Spatial Data Structures.
In Insert mode, click and drag to specify a new rectangle, in Delete mode click inside an existing rectangle to remove it from the quadtree. In Search mode click and drag to specify a rectangle. Rectangles in the quadtree that overlap the specified rectangle will be shown.