Root's structure was indeed as Shigaraki Tanuki had described.
In the original story's setting, the Anbu under the Hokage had a clearly defined organization: 70 members divided into five units of 14. An Anbu Captain, such as Hatake Kakashi in later years, led the other 13 members, while squad leaders commanded the smaller squads within each unit.
In theory, Root had only 14 members, including Shimura Danzō, but in practice, it could never have had so few.
Taking advantage of the war, Root was expanding frantically to meet Konoha's demand for intelligence. After the Nine-Tails Incident, Sarutobi Hiruzen realized that Root had grown too powerful to control and decisively disbanded Danzo's Root.
In reality, however, the people removed... numbered just 14.
The gesture meant more symbolically than practically.
Even so, at this point in time, those 14 positions still carried considerable weight. Within Root, competition for the 13 seats other than Danzo's was fierce.
From their current perspective, both Aburame Ryūma and Shigaraki Tanuki believed Hyuga Yu had joined Root to become one of those 13.
And now,
Through Shigaraki Tanuki's circumstances, combined with his extensive experience from his previous life in forming cliques and suppressing rivals, Hyuga Yu finally understood the "factions" he had sensed within Root.
Unlike the later Root, whose members were all dismissed by Sarutobi Hiruzen and had no choice but to follow Danzo down a road of no return, Root at this time still offered some hope.
After all, even Danzo was theoretically just an Anbu Captain.
There were five such captains, all appointed directly by the Hokage.
And given that Danzo was missing an arm, a leg, and a few brain cells, who knew when he might retire? Who would become the next captain of Root then?
Aburame Ryūma had probably assigned him to