It’s easy to measure the height of your trees with your arm and a stick.
First, measure the distance from your eye (or forehead) to your finger tips with your arm extended at eye height. Mark a stick at that length (or break it to length if it’s too long).

mark at eye height. This tree is 139 feet tall!
With your fingers, hold the stick out in front of you with your arm fully extended. The stick should be vertical and the mark or broken end held at eye height.
Walk away from the tree until the tip of the stick lines up with the top of the tree and the bottom of the stick lines up with the bottom of the tree. Try to keep the mark at eye height and rotate your eyes rather than your head when lining up.
The distance from your eye to the base of the tree is equal to the height of the tree. Pace off the distance from where you’re standing to the base of the tree. Multiplying the number of steps by your step distance equals the height of the tree. Golfers will know the exact distance quickly. If you don’t know your step distance, calibrate your steps by counting your paces while walking for a known distance (the width of your house for example). Your step distance is the distance walked divided by the number of steps.

Angle D = 90°
Side AB = Side BC
Side AD = Side DE