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This phase orders the nodes of each level by separating the children of nodes into leaves and inner nodes. Inner nodes are arranged near the middle of the level, with the heaviest node in the middle. It then fills whitespaces in the levels with corresponding leaves. It starts two levels above the deepest level, because the deepest level contains only nodes and therefore no reordering is necessary. And the level above the deepest level contains only children of the level above, which are ordered by the their parents.
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