Poke about in wee tree (8)
I believe the answer is:
pedigree
'tree' is the definition.
(thesaurus)
'poke about in wee' is the wordplay.
'poke' becomes 'dig' ('dig' can be a synonym of 'poke').
'about' becomes 're' (regarding**).
'in' is an insertion indicator.
'wee' becomes 'pee' ('pee' can be a synonym of 'wee').
'dig'+'re'='digre'
'digre' placed inside 'pee' is 'PEDIGREE'.
(Other definitions for pedigree that I've seen before include "Line of ancestry, particularly a distinguished one" , "Lineage, ancestry" , "Line of decent or ancestry" , "Pure lineage" , "List of ancestors" .)