do not wait until winter - trim now
the 18-inch stump was ..... chosen poorly
it should have been clear cut at the ground
too late now - if you don't have a chainsaw find someone who does and make a 75-degree angle cut then cover the exposed wood with the tree goop and keep it covered
in 5 years it will get absorbed in to the main trunk
the 2 offshoots should be cut like this:
then everything below the red V comes off - you are diverting the growth power of the root system sideways - this is why the upper stalks are long and gangly
note the red rectangle - that's cross-growth - unsustainable as the branch it is attached to becomes heavy - and then in an ice storm can take down everything below it
look for cross-growth AND duplication especially in the yellow zone - pick winners and losers that will have space to expand and are growing up and out at 30-45 degrees from the branch - 2 branches growing the same direction 2 inches apart - pick one
losers: duplication, cross-growth, branches growing "backwards" toward the main trunk, sucker-growth on the main trunk - if it is not going to be a primary branch clean it off every 3 months and finally anything that's not growing sideways or up
winners: symmetrical, sideways, up, forward - let all of this stay for now no matter how tall/long/spindly - in 2 years you will then begin to shape for the 25-year target; also if you find sucker growth on the main trunk that is where you would want a branch to be - LEAVE IT - you will have the infant branch a year from now when you divert the growth power 100% to winning wood
the tree will fill in as it fills out - give it the help it needs to send all of it's growth power in a symmetrical out/up pattern
you should have started 3 years ago but you can recover
finally - the tree ring at the ground - rip the grass out and dig out the roots in the white circle - go 6 inches down or until you find roots - i can tell you how to build a 50-year tree ring yourself or have a landscaper do it but you have to get that grass off the root system - at least 5 feet diameter stone circle - then fill it with 6 inches dirt and 6 inches cedar mulch