I planted a eucalyptus at the end of my garden some 15 years ago, and (after
chopping the top 6ft each year) it is now ideal for a good tree platform for
my 5 yr old.

I have some 4x2 beams and have identified some good mounting positions, to
these I plan to screw some old floorboards.

But what is the best way to fix beams and planks to a tree? I don't fancy
nailing into it as that seems unkind, but I am not sure that typing with
rope is going to be sufficiently secure for when all his friends get up
there!

Many thanks for any suggestions,

Laurence