Leaves of my models becoming invisible?

I made this willow Tree model in blender and when i apply my textures i get this effect where parts of my texture become invisible from certain angles i've went into blender and duplicated all the "cone shapes" essentially in hopes that would fix it but it did not. is this something i can fix in Unity or do i have to fix this in Blender im stumped please help thanks. picture below.

 

From what i can see, i looks like your problem is "backface culling"
In Blender by default, faces are displayed as double sided. (N panel, shading, backface culling)
In Unity, most shaders are single sided. So you need a different shader that renders double sided, or you need to duplicate those faces, and flip the normals.

Hope it helps.