The 'SPREAD MODE' allows you to increase or decrease the angles of adjacent terminal branches or all angles within subtrees.
Click on the tenth button in the left column of the 'ARB_NT' window to activate the 'SPREAD MODE'.
To spread all angles of a subtree, click and drag a branch towards the tips of the tree.
To reduce the angles, drag towards the tree center.
To reset the spreading of a subtree to the default value, press the key '0' (zero) while pointing to that subtree.
To reset the spreading of the whole tree, point somewhere outside the tree while pressing zero.