There at the remains of at least three pairs of branches on the trunk below the top branch.
My guess is that your kids' football has "pruned" this tree severely. You can either treat it as an "interesting" shape (which has a certain "Japanese" feel to it!) or if you want a conventional shaped tree, buy another one and protect it from flying missiles.
If you want to convert the existing tree into a normal shape (for example by getting rid of one remaining branch after a year or two, when the top has grown more), at best you are going to have a tree with long bare trunk which will probably be more at risk from blowing over in high winds, etc.