Trees, Shrubs and Conifers: Help with this tree!, 1 by Resin

Resin wrote:
Played photoshop with your last photo - shows that it is missing a substantial area of bark near the base. Looks like it got hit by a vehicle a few years ago. That makes the tree open to decay, and potentially dangerous in the longer term. That will be your best option of getting the city to remove it legitimately.

Sorry, but I don't think you should make any attempt to kill it off yourself - very likely to be illegal, and could result in a substantial fine or jail time if found out (and city authorities will investigate suspicious tree deaths!).

Resin