Depends how you want your plant to grow
if you just have lights on the top of the plants after a while the bottom isn't going to get any light and you're just going to grow tops after a while
if you want your plant to grow all around you can stick some bulbs on the sides of it and during veg. those sides will also grow so your not really wasting any of the tree since the side bulbs will also be giving light to the bottom leaves.
it all depends on how you want your plant to grow =)