All of the fruit are close or touching each other.

Unity Through Repetition; They repeat an element, a size, a shape, a texture, a color or a motif throughout the composition.
In this picture; everything is the exact same.

Unity Through Continuation; When the artist continues something, usually a line, an edge, or a direction from one object to another the viewer’s eye is carried smoothly from one thing to the next. Because of the way objects are placed, the viewer’s eye movement connects the objects.
In this one; it's a line of dominos, falling continuously.

Unity With Vareity; This prevents the composition from being boring.
In this one; it's one picture, with different colors, in different places, than the last one.

Intellectual Unity;
Sometimes parts of a composition don’t look unified at all because there is no repetition, continuation or proximity. We recognize that the objects go together because of what we know about them.