Even if it were truly possible for the Barrier of the "Life Tree" to completely enclose the entire Star System, by then the size of the tree would probably not be smaller than the whole Blue Star. It would become a planetary celestial organism like the "Giant Turtle Star," and it's uncertain whether Blue Star Humans could withstand such a massive change in living space; the civilization's technological path would also face a tremendous challenge.
Even Chen Fei himself couldn't imagine everyone living on a giant tree—what if someone didn't think it through and decided to drop a "Tsar Plus" on it... To be honest, without the Barrier Domain, the "Life Tree" itself isn't more damage-resistant than Blue Star.
