Poisonous tree left active? Set fire to ‘em, I say (8)
I believe the answer is:
laburnum
'poisonous tree' is the definition.
'laburnum' can be an answer for 'tree' (type of European tree). I'm not sure about the 'poisonous' bit.
'left active? set fire to 'em i say' is the wordplay.
I cannot really understand how this works, but
'left' could be 'l' (common abbreviation) and 'l' is found in the answer.
'active?' could be 'a' (grammatical abbreviation) and 'a' is found within the answer.
'fire' could be 'burn' (synonyms) and 'burn' is located in the answer.
The remaining letters 'um' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for laburnum that I've seen before include "Poisonous shrub with yellow flowers" , "Plant with hanging clusters of bright yellow flowers" , "Poisonous flowering shrub - run album (anag)" , "Tree or shrub with bright yellow flowers" , "Ornamental tree with hanging clusters of yellow flowers" .)