Update..

..he's decided that
the slopey trees offer the 
best chance success!

Leo's arboreal adventures continue!
Maybe he could just walk up a tree like this one!  Which reminds me of Older Teen's similar attempts aged about four.  One park we used to go to he would only refer to as 'the park with the slopey tree', which he was desperate to climb but would abort as soon as his feet were off the ground!  Perhaps I should go back and see what Leo makes of it, even without opposable thumbs he would probably make a better fist of it :-)  
Mr KCNQ2Haiku is in Edinburgh for a few days so I'm Ben monitor and I'm off to watch him play Minecraft, wish me luck!