A 50 m rope through the boul will do it but allow more if you want to belay someone back from the anchor point, e.g., Petzl ID in lock at the anchor point. Get the rope through the boul for a good start. There is no need to climb above the boul but you probabley wont see the cache from the ground (thats why its D5). This tree has very little in the way of side branches so can not be done by free climbing or off a ladder. The cache is tied into a small none loading bearing branch easily reacable from a weight bearing side branch. It has been placed where birds will not nest.
The tree is a lonish oak with a holly bush to its south. Its near but safely off a public foot path.
FTF: Citrus Lizard