Mock orange tree
If possible, send me photographs of your tree. I am assuming since you are in Hawaii that your Mock Orange is Murraya panicula. In the continental states, mock orange is an ornamental shrub.
The ants might indicate the presence of sap-feeding insects like aphids and scales. You can check the foliage and stems for sticky droplets of syrup. Sap feeders tend to not use all the sugar they take in from the tree's sap and excrete it. Also, the sugary droppings may cause a mold problem called sooty-mold to happen. This looks like black dust over the foliage and stems.
Dead branches can mean many things. Cankering fungus could be invading the stems; the tree may have experienced some root loss and no longer has enough water coming in from the roots to maintain itself. This usually results in dying back from the outer branches. Also, stem girdling insects or stem boring insects could be present.
Roots showing above the soil that were not there before could be an indicator of erosion. Rainfall does steadily move small amounts of soil and this will expose roots.
I strongly suggest trying out the Hawaii Cooperative Extension and discussing your problem with them. Here is their web address.
Look over your tree with the notes above and see if any of it is a match. Then discuss it with your local extension agents.