It's possible that they can be "scale insects". If there is a sticky film on the lower leaves then it more than likely is. They can be picked off by hand then apply a insecticidal soap. It can sometimes be hard to get rid of them.

I agree with everything tony c m said.

I would clip off the affected leaves and pick off what I can on the insect with my fingers on the rest of the tree and spray everything I can on that tree.

You did not mention if your tree is in a pot or in ground.
If it is in the pot then spray the pot too and keep it away from other plants. Repeat this a couple more times within a week or ten days and you should see good results.

I use Safer Brand Garden safe insect soap. It is non toxic and made of seaweed extract. Get the concentrate so it will be cheaper in the long run. The bottle is like Aqua color and the cap is Purple.

Had this problem a few times with new trees but seems to not return after the first Winter here in Michigan.

Good luck