You can browse the gallery by clicking on the arrows shown on the first or the last of the tree pictures shown in the gallery.  A click on these arrows will bring you to the next tree or previous tree pictures in the gallery.

You can view the pictures in full size by clicking a picture of your choise.  This will open the picture in a new floating window  -  and here you can go to next picture or previous picture by clicking the right or left arrow on your computers keyboard.