A Thousand Dancing Frogs
From Discworld MUD Wiki
It appears as a jade leaflet.
This is a single jade leaflet. It seems to be a type of book, yet still part of the grand willow. This leaf is still connected to the willow by a single platinum stem, yet something ominous tells you this leaf is here to stay. The platinum lining of the leaf sparkles in the available light and sends dancing shimmers across all the other leaves and branches. Octarine sparkles dance and shimmer atop the jade leaf.
This book hangs on the sixth level of the willow in the courtyard.
You will need some tree climbing skills to climb the tree up to it.