code: def to_grid(self):
      grid = []
      current_height = self.height
      frontier = self.children
      while any(x.height != current_height for x in frontier):
          new_frontier = []
          row = []
          grid.append(row)
          for x in frontier:
              if x.height == current_height:
                  row.append((x.name, x.width))
                  new_frontier += x.children
              else:
                  row.append((None, x.width))
                  new_frontier.append(x)
                  frontier = new_frontier
          current_height -= 1
      row = []
      grid.append(row)
      for x in frontier:
          assert x.height == current_height, (x.height, current_height)
          assert x.width == 1, x.width
          row.append((x.name, x.width))
      return grid
  
imports: from ..expr.types import tstruct
label_desc: Use image node_id 4 for calling the PlacementTree obj's underlying member method code with example usage: obj.to_grid() and returns: grid