Just when it looked like the trespassing tree-sitter siege in Berkeley was winding down, up pops another law-breaker to join the remaining trio.

Oh, and a police officer was attacked by one of the tree-sitters’ supporters.

Ho-hum.

I remind you again that these loons have been perched in the branches since December 2006.

Dumpster Muffin must be proud:

A fourth tree-sitter has joined three remaining protesters living in the branches of an oak grove outside Memorial Stadium, a university spokesman said today.

The man, whom university officials did not identify, climbed over one fence Sunday night and up a different tree from the one occupied by the other tree-sitters, UC Berkeley spokesman Dan Mogulof said.

Also Sunday, campus police arrested a 56-year-old supporter of the tree-sitters on suspicion of battery on a police officer and resisting arrest. David Walton was trying to get supplies to the tree-sitters when he got into an altercation with an officer and threw the officer to the ground, Mogulof said.

Last week, four of the tree-sitters left the trees, leaving three remaining protesters. The group is protesting the university’s plans to cut down the oak grove to build an athletic training center.

The latest tree-sitter went up Sunday with a pack of supplies.

“It’s his intention to stay as long as he can … to save the trees,” said Doug Buckwald, a spokesman for the protesters, who said the man is in his 30s.

No, they don’t have anything better to do.