If possible let T+e1+e2+e2 be non planar Then either one of e1, e2 or e3 or T must be in another plane T is a tree of order atleast 4. i.e maximum number of children per root is more than or equal to 4. Hence vertices containing e1, e2, e3 have to be planar. T being a tree with root is also in the same plane Hence proved Solution If possible let T+e1+e2+e2 be non planar Then either one of e1, e2 or e3 or T must be in another plane T is a tree of order atleast 4. i.e maximum number of children per root is more than or equal to 4. Hence vertices containing e1, e2, e3 have to be planar. T being a tree with root is also in the same plane Hence proved.