Treemaps by default limit the max number of drawable children (top levels) to 10. You can modify this by setting
options to be equal to the max number you wish to draw.
However, in some cases of data, that may not completely solve your problem. ZingChart will attempt to draw the rest of the nodes but if there are drastic ranges in your data, that will prevent the small nodes from being drawn.
Refer to the Treemaps Tutorial for more information.