A tree near rear of house is burning (5)
I believe the answer is:
afire
'is burning' is the definition.
(thesaurus)
'a tree near rear of house' is the wordplay.
'tree' becomes 'fir' (fir is a kind of tree**).
'near' says to put letters next to each other.
'rear of' suggests the final letters.
The final letter of 'house' is 'e'.
'a'+'fir'+'e'='AFIRE'
(Other definitions for afire that I've seen before include "Ablaze" , "Alight" , "lit up" , "Burning" , "in flames" .)