Expand/Collapse clue on a chart

I am currently working on an org chart with collapse/expand capability. In case it matters, the original code is from d3/visx. To improve user experience, I want to include a clue that a node can be expanded or collapsed. In my example below:

• "Software Lead" can be expanded
• "Project Manager", "Business Analyst" and "Hardware Lead" can be collapsed
• "Sponsors" cannot be expanded

For now I have added a red/green dot in the top right corner of each active node. Does it make sense? Is there a better way?