Ideal Start:
1 copy of one for one/lonefire blossom or a copy of rikka petal/the rikka spell that can search out a rikka card
Once petal is summoned, depending on hand search out the level 8 rikka that can ss itself with another plant monster in hand to go into rank 4/6/8 plays(Ideally ss the level 6 that can search out the rikka spell/traps.)
You can also go into the rank 4 rikka xyz to recover a rikka card in the graveyard, which you can tribute with either the rank 8 or any of the rikka spell/traps to ss divine treebeast via its own effect, or into other rank 5 or higher plant xyz depending on the board.