There are several different ways to view an open breakdown structure.

There are several right-click menu options available in a breakdown structure view.

Select the cogwheel icon to access these options.

Select the split box icon to split the breakdown structure view. This allows you to easily drag a task from the lower part of the tree structure to the upper part of the tree-structure, as shown here.

Select the solid box icon to set the view back to non-split mode.