Much like the definition of “stick up your ass,” this is used to describe a strict person - however, this version describes it to a rather extreme extent.
cat stuck up a tree refers to news, especially local news which is utterly pointless and of no interest to anyone whatsoever but talentless hacks put it on the tellynevertheless.
talentless hack from Border Television's Lookaround: "We are coming on live and exclusive coming from Hawick where there is a cat stuck up a tree"