# Pastebin RV75koPe
COMMON-LISP-USER> (defparameter tree '#2=(#1=(a) (b c a #1# #2#) . #2#))
(setf *print-circle* t)

TREE
COMMON-LISP-USER> 
T
COMMON-LISP-USER> (print-identified-conses tree)
#3=(#1=(#2=A . ()) . ((B . (C . (#2#  . (#1#  . (#3#  . ()))))) . #3# ))
#1=#1#
COMMON-LISP-USER>