<｜begin▁of▁sentence｜>### Instruction:
As a legal secretary working for a law firm that deals with land acquisition cases, one of your tasks is to assist the legal team in creating visual representations of tree diagrams for property boundary disputes. You need to use igraph's Cairo drawing backend to set a custom bounding box of 600 by 400 units for the drawing area and then save the visual representation of the tree as 'tree.png'. This will help the legal team better understand the spatial layout of the properties and assist in the resolution of the disputes.
### Response:
from igraph import Graph, plot
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