As FFGhost reported, there was an article in the 15th March 1935 Watchtower entitled "Prophecy of the Trees" (pp.83-90). In part it says (para. 7) :
Both good and bad trees appear in this prophetic parable recorded in Judges nine. In symbol the inanimate objects represented the following :
The olive tree in the parable symbolically pictured Gideon, Christ Jesus, the Greater Gideon, and the faithful remnant.
The fig tree symbolically pictured Jether, the first-born of Gideon, and the “holy nation”.
The vine symbolically pictured Jehovah’s royal house, Christ Jesus the Head thereof in charge of the royal house, together with the others who will have a part in the vindication of Jehovah’s name.
The bramble, or thorn tree, in the parable symbolically pictured the visible rulers of this world that constitute the official element of Satan’s organization in the earth.
Abimelech, the bastard son of Gideon by his concubine, played in the drama the part of the active and visible ruling elements of the world since 1914.
Shechem, the city and the residents thereof, particularly the Levites, pictured the religious element, that is, the clergy element of “Christendom”, including “the man of sin” class.
The “seventy sons” of Gideon pictured the followers of Christ Jesus engaged in doing the Elijah work of the church prior to and up to 1918.
Jotham, the son of Gideon who uttered the prophecy of the trees, pictured the remnant.