to set a climbing line in a tree and secure it with an appropriate hitch or device.
Merriam-Webster Online Dictionary
tie in (verb)transitive verb
to bring into connection with something relevant as
a) to make the final connection of - tied in the new branch pipeline
b) to coordinate in such a manner as to produce balance and unity - the illustrations were tied in with the text
intransitive verb
c) to use as a tie-in especially in advertising to become tied in