Now you have to adjust the vertices at the ends to give the tread some curvature at either side.
You can leave the tread like it is and go to the next step if you want because what I'm about to suggest will add a LOT of polys to the tread, especially since you are clone this thread about 40 or 50 times.
Anyway select the red edges and chamfer them by 0.2 or whatever works for you. The reason I chamfer them is so that the corners can catch the light realistically when rendered. It's up to you whether you want to do this or not.
Now we have to clone the tread pattern a number of times. In the menu, select Tools->Array to open the array dialog box. The picture shows the settings I used but you will have to test the value you put in the red box because it's going to be different for everyone. You want to use a value that will place all the treads right next to each other with no overlap and no gaps. Play with it and you will get it right.
When you have got it right, you have to attach all the pieces together. Select the original piece and click the little button next to the "Attach" button (shown in the red box) to open the Attach List. Select all the tread pieces in the list and then click "Attach." Now the pieces are all one piece of geometry. Add a "Vertex Weld" modifier from the modifier list and test different values for the threshold. This will weld any overlapping vertices automatically without you having to go through and do them one by one.