Step 1:
The paper for the trunk with branches is 30x30 centimeters. I used 50x50 cm papers for the larger trees.
Prefold in half four times.

Step 6:
Fold this edge downwards.

Step 5:
Prefold over these two lines.

Step 2:
Fold over the two lines at the bottom right, then over the two diagonal lines. And then over the two lines at the top left. All folding lines are prefolded.

Step 4:
Squash-fold the flap.
Repeat step 3 and 4 on the other three flaps.

Step 3:
Fold one flap straight upwards.

Step 10:
Fold the little triangle flap inwards.

Step 8:
Fold the little triangle flap upwards.
Repeat steps 5 to 8 on the other three same places of the model.

Step 9:
Pull open

Step 7:
Press / fold these edges downwards over the prefolded lines.

Step 16:
Bookfold one layer

Step 15:
Press inwards, into the same shape as step 12 again and now with the center folded inwards.

Step 12:
Prefold over this line and open the model.

Step 11:
Close the model again.
Repeat steps 9 to 11 with the other three triangle flaps.

Step 14:
Make sharper folding lines

Step 13:
Sink-fold the center over the prefolded line(s).

Step 21:
Fold this flap upwards and a little sidewards.

Step 19:
Fold this flap upwards a little.

Step 20:
Turn the model.

Step 18:
Fold the flap sidewards

Step 17:
Fold over these two lines. Repeat on the other three sides.

Step 22:
Fold this flap into a small angle, it stays almost straight upwards.

Step 28:
Fold the flap inwards

Step 25:
Fold over the two lines at the bottom right, then over the two diagonal lines. And then over the two lines at the top left. All folding lines are prefolded.

Step 26:
Fold over the two short lines first, then over the two longer lines. Make the same folds on the backside.

Step 24:
I used six green papers in various sizes and tints for the crown, you can make them in any size you like best.
Prefold in half four times.

Step 23:
Done...

Step 29:
Repeat step 28 on the other three flaps.

Step 27:
Open the model / make it 3d

Step 30:
This is how the model looks from below

Step 31:
Done, make about six of these crown parts in various sizes and greens.

Step 32:
Glue the crown parts to the trunks.

Step 33:
Make sure the tree remains in solid balance, you can pull the base of the trunk outwards to get more balance.

Step 35:
I glued the smaller parts on top of the lower larger parts.

Step 34:
Here I folded the tip of a branch sidewards and glued a crown part on it.