He’s right beside the tree (6)
I believe the answer is:
oliver
'he's right beside the tree' is the definition.
The definition suggests a singular noun but the answer is not.
'he's right beside the tree' is the wordplay.
'he's right' becomes 'r' (I can't explain this - if you can you should believe this answer much more).
'beside' says to put letters next to each other (I've seen this in other clues).
'the tree' becomes 'olive' (olive is a kind of tree).
'r' after 'olive' is 'OLIVER'.
Can you help me to learn more?
(Other definitions for oliver that I've seen before include "First name of Dickens boy Twist" , "Fictional boy who famously asked for more" , "Hardy, maybe" , "Roland companion; Bath biscuit" , "Dickens-based musical" .)