Real trouble concealing lord's last tree (5)
I believe the answer is:
alder
'tree' is the definition.
(I know that alder is a type of tree)
'real trouble concealing lord's last' is the wordplay.
'trouble' is an anagram indicator.
'concealing' indicates putting letters inside.
'last' suggests the final letters.
The final letter of 'lord' is 'd'.
'real' anagrammed gives 'aler'.
'aler' going around 'd' is 'ALDER'.
(Other definitions for alder that I've seen before include "Native tree" , "Tree or shrub whose wood is resistant to underwater rot" , "Artificial fishing fly" , "One [TYPE OF TREE]" , "Tree akin to the birch" .)