I get concrete test beams from Texas Dept. of Transportation.....
Any road job has them.... and the contractor is glad for you to haul em off..
They are 6" x 6" x 22" and weigh about 55# each.....
I drill a hole through the blocks and run a nylon rope through both blocks and tie a knot... It will not pull through the hole....then tie to the bottom of the tree.....
I use trees 6' x 8' tall..... Tie a 2.5 gal plastic jug in the top to keep the tree upright at all times....
Farmers get chemicals in these jugs.... I triple rinse with a little soap & water and they are good to go.....
It takes 2 concrete blocks to do a good job of sinking the tree....
It works great for me....
Hope this helps.....
PM me and let me know...
Good fishing.....