Tree bottom invisible

In blender, the bottom of my trDesktop Screenshot 2020.10.20 - 09.42.15.10 (2)

In blender, the bottom of my tree appears, but in Roblox, its invisible. Help?

Adding a Solidify modifier can fix this issue, because Roblox only renders one side of the mesh(if you turn on face orientation mode, Roblox only renders blue sides).