There are 3 trees that you can climb into on Wasteland. All 3 are identical.

The trees are split into 2 boles, they are the only trees like this in Wasteland.

Tree 1: By the helicopter, between the heli and the exploded Hummer.

Face the tree so that the hummer is to your left and the heli is to your right.

Run/jump at the base of the tree where it splits. It is quite difficult and annoying, but will eventually let you jump on. Climb out the branch toward the heli as far as it will let you. Turn to face the other branch, jump as high up as you can (about 5 fake branches stick out of the area that you are jumping to). Turn to face the first branch and jump to the highest point you can. You will be inside a part of the tree as from here on up, both sides are fake and you will fall out if you try to go higher. Tree 1 is a good spot, there are only 2 ways that you can be approached and you are fairly hidden from sight.

Tree 2: This one is between the heli and the house with no roof with a cemetery behind it. You are easy to spot in this tree, I do not recommend it.

Tree 3: This is between the house with no roof and the golden statue. This tree is also a good one to hide in as you are well hidden and have a great view of most of the area there.

Tree 3 has an alternate method of getting into it if you are having no luck jumping into it: get on the broken wall behind the roofless house, jump onto the low back overhang roof of the roofless house. Turn right and run/jump to the broken cement column. Jump to the intact section of wall near the tree. Get on the corner of the wall and face the tree. Jump onto the white tri-cross gravemarker to the left of the dead cow. Face the tree, back up as much as you can on the gravemarker, run/jump to the lowest part of the tree. Follow directions from tree 1 to get up higher.