public static @NotNull ActionCallback movePageDown(final @NotNull JTree tree) {
    final int visible = getVisibleRowCount(tree);
    if (visible <= 0){
      return moveEnd(tree);
    }
    final int size = tree.getRowCount();
    final int increment = visible - 1;
    final int index = Math.min(getSelectedRow(tree) + increment, size - 1);
    final int top = getFirstVisibleRow(tree) + increment;
    final int bottom = top + visible - 1;
    return showAndSelect(tree, top, bottom, index, getSelectedRow(tree));
  }
public static @NotNull ActionCallback movePageDown(final @NotNull JTree tree)