Dutch design crew Sam van Veluw and Rogier Martens a.k.a Andeboom have invented the "P-tree", a portable urinal unit that can hang off any tree. They're currently all over the Roskilde festival in Denmark, because at festivals people will urinate against trees no matter what. Might as well sort them a target. It's funny how the Dutch excel at temporary urinal solutions designs, as I recall the first FUD (female urination device) I saw came out of Holland, now there's she wees and go-girls and who knows what else. You don't need to buy gadgets though, you need to master "the arc" s'all. (NSFW language and a bit of TMI if you're a boy).
The P-tree is a temporary tree-friendly urinal that can be fixed on every tree using straps and lashings. The P-tree gives a feeling of freedom during peeing. It is the same as peeing into the wild. The hoses from the urinal can be combined and connected on a waste pipe with container. The P-tree is very accessible for festivals, public gardens, events, etc. P-tree and Lashings are available in different RAL-colors.