In level layout mode with flow direction to the top or
bottom, the nodes are organized in horizontal levels such that the
nodes of the same level are placed approximately at the same y-coordinate.
The nodes can be justified, depending on whether the top border, the
bottom border, or the center of all nodes of the same level must have
the same y-coordinate.
In flow direction to the left or right, the nodes are
organized in vertical levels approximately at the same x-coordinate.
The nodes of the same level can be justified at the left border, at
the right border, or at the center.
To distinguish the level alignment independently from
the flow direction, the directions north and south are used (see Using compass directions for positional layout parameters
(TL)). The north
border of a node is the border that is closer to the level where its
parent is placed, and the south border of a node is the border that
is closer to the level where its child nodes are placed. If the flow
direction is to the bottom, the level alignment north means that the
nodes are justified at the top border, and south means that the nodes
are justified at the bottom border. If the flow direction is to the
top, north and south are inverted: north means the bottom border and
south means the top border. If the flow direction is to the right,
then north means the left border and south means the right border.

Level alignment
To specify the level alignment:
Use the method setLevelAlignment:
treeLayout.setLevelAlignment(ibm_ilog.graphlayout.tree.TreeLayout.NORTH);
The valid values for levelAlignment are:
ibm_ilog.graphlayout.tree.TreeLayout.CENTER
(the default)ibm_ilog.graphlayout.tree.TreeLayout.NORTH
ibm_ilog.graphlayout.tree.TreeLayout.SOUTH