The project scheme section on the estimate page helps visualize the site for the crew. This is especially useful for complex workorders with several services involved and/or locations with multiple trees. Besides, you can mark potentially dangerous places on the site for the crew to avoid them.
To leave the marks on the project scheme, first upload the item icons. These are small images which will help you and the crew to distinguish the services and locate the tree. They can be uploaded in the Estimates Scheme Items section:
To delete an existing icon from the list, click on the basket here: 
To see the items in action, create a project scheme on the estimate page.