Filter the pages: type "tree" in the filter panel and search. The number of matches is 2, but depending on the resolution of the screen, they will not be plotted. Try resizing your browser window to notice that. This can be seen in the attached image.
In the image it can also be seen (see the dashed line of the lasso selection) that there is a big gap between the borders of the plot (square dense line) and the area that the pages are actually plotted.
The visualization panel sometimes doesn't show all pages that are close to the borders. Steps to reproduce: