Hi,
Welcome to our forum and thanks for contacting us with your question.
In our API there is a setting responsible for whether the grid node belonging to this point should start as collapsed.
https://api.highcharts.com/gantt/series ... .collapsed
Gantt demo with collapsed task:
https://jsfiddle.net/BlackLabel/us3ykpzt/
Feel free to ask any further questions.
Best regards.