Two graduates introducing book about old African tree (6)
I believe the answer is:
baobab
'african tree' is the definition.
(I've seen this before)
'two graduates introducing book about old' is the wordplay.
'two graduates' means two replacements for 'graduate'.
'graduate' becomes 'ba'.
'graduate' becomes 'ba'.
'introducing' suggests taking the first letters.
'about' is a charade indicator (letters next to each other).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
The initial letter of 'book' is 'b'.
'ba'+'b'='bab'
'bab' put after 'o' is 'obab'.
'ba'+'obab'='BAOBAB'
(Other definitions for baobab that I've seen before include "Monkey-bread tree" , "African or Australian tree with very thick trunk" , "Tree indigenous to Africa and Australia" , "Growth seen in Africa" , "The monkey bread tree" .)