To show what we want to do, i got this bush.
left: without detail bending, right: with detail bending
This is wrong. Its to unregular. It will breack our bending.
If this is done we have to turn on Vertex Channel Display in Object Properties. Now our object looks like it got no shading. To sea only the vertex color we put on a white material.
Now we assign the first vertex color modifier and paint the hole object black. The first modifier is for the up and down movement of each leaf. For this we use a clear blue. Its very important that we got a 100% clear blue without any red or green. 255 blue means that we got no bending here. 0 blue means strongest bending. So for this object we can select the middle vertexes and turn on soft selection in vertex paint menu. We choose a value so that we got a soft selection all over the object by only selecting the middle vertexes.
Now we give a 255 blue on this selection and got this result:
Now we assign a second vertex color modifier which is not regular bending on the sides of each leaf. First we paint all black again. Than we select the outer vertexes of each leaf and paint them 255 red which means here is maximum bending. Than we take the vertexes one more inside and give tham a 128 red for lower bending. To get some more variations in this bending we can take some outer vertexes and give them a 220 red. The most important is, ceaping the middelline total black and use only pure red.
Our last color is green. We assign a new vertex color modifier (_don't collapse the other two_)and got to element mode. Now we select our first leaf an paint it green 255 green (again only green, no red nor blue). Than paint the next leaf 220 green, next 190, next 170 and so on. its not important to have exact values, just make sure you use a lot of different greens. This color tell the leafs to start bend in different times, so not all together going up and down.
If this is done we set the red and the green vertex paint modifier to "add" mode in the vertex paint dialog. To get this result: