Like a chimp pair, regularly in tree (5)
I believe the answer is:
apish
'like a chimp' is the definition.
(I've seen this in another clue)
'pair regularly in tree' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'in' is an insertion indicator.
'tree' becomes 'ash' (ash is a kind of tree).
The alternate letters of 'pair' are 'pi'.
'pi' put inside 'ash' is 'APISH'.
(Other definitions for apish that I've seen before include "Foppish" , "Stupid" , "Silly" , "Foolish; simian" , "Foolish; like a monkey" .)