Everyone familiar with Anthony knows that when talking to this Old God Stick, you must stay on high alert, as his words are full of traps. If you're not careful, you'll fall for them, just like now.
He clearly knows that when the Deceit Tree talks about leaving here, it's not just referring to them, but mainly to the Master of Stars who's been hammering it so hard that it had to flee. However, Anthony naturally ignored this point with a well-reasoned argument, 'That guy is so strong, how could he possibly be one of us.'
The Deceit Tree internally accepted this reason. Ange is indeed powerful, able to anchor its consciousness and reach its true body. The Undead King is also very strong, so much so that it doesn't even dare to think of fighting him. It's hard for two such powerful beings to join forces; neither would yield to the other.