You can drag and drop additional images into the lower part of the Images Pane, called Augment Reconstruction. For each batch of images, a new Group will be created in the Images Pane. You can drop successive batches of N images in the Images Pane. for each batch of images the graph will branch.
You can use this method for complex scenes with multiple objects
The groups will be merged using the ImageMatchingMultiSfM node. Read the node description for details