A simple first stab at building a bounding-box style collision detection rule for d3V4 forceSimulation. Bounding box is a rule that produces a top-left and bottom right corner with coordinates local to the center of the node. So, in this case the size of the bounding box is fixed at a height of 20px offset by 10px and a variable width based on the length of the label of the node.
https://d3js.org/d3.v4.min.js