cl-copy-tree is an alias for `copy-tree' in `cl.el'.

(cl-copy-tree TREE &optional VECP)

This function is obsolete since 24.3;
use `copy-tree' instead.

Make a copy of TREE.
If TREE is a cons cell, this recursively copies both its car and its cdr.
Contrast to `copy-sequence', which copies only along the cdrs. With second
argument VECP, this copies vectors as well as conses.