Robert and Jack circling area to get tree (6)
I believe the answer is:
baobab
'tree' is the definition.
(baobab is a kind of tree)
'robert and jack circling area' is the wordplay.
'robert' becomes 'bob' (short for Robert).
'and' says to put letters next to each other.
'jack' becomes 'ab' (both can mean a sailor).
'circling' is an insertion indicator (circling can mean going around or containing).
'area' becomes 'a' (maths abbreviation).
'bob'+'ab'='bobab'
'bobab' placed around 'a' is 'BAOBAB'.
'to get' is the link.
(Other definitions for baobab that I've seen before include "Growth seen in Africa" , "African fruit tree" , "Tree indigenous to Africa and Australia" , "The monkey bread tree" , "African or Australian tree with very thick trunk" .)