You could try using a guy cable loosely looped and padded around the trunk at the position of the first branch - the cable should then be fastened to a post that is well secured. To pull the tree upright it would be advisable to excavate under the base of the tree, exposing the roots until the plant is sufficiently loose in the ground to allow movement. Winter is the best time to attempt straightening the tree but make sure that you keep the plant well watered throughout the first summer after excavation. Is there any thing that can be painted onto the stump which is not harmful to animals. The most guaranteed method is to remove the stump or hire an arboriculturalist to grind the stump out.
Chemicals are generally less satisfactory and are all toxic.
There are several brushwood and stump killers on the market and are available from garden centres. The majority rely on either spraying the healthy shoots or drilling into the stump top and pouring the chemical into the holes. Most require several treatments over more than one season to be effective. More expert advice on trees and shrubs . For specialist advice, send your questions to our team.