Materials Needed:

Worsted weight yarn in green (or your desired tree color)
Small amount of yarn in various colors for decorations (red, yellow, blue, etc.)
Crochet hook suitable for your yarn (size G/4.00mm works well with worsted weight yarn)
Yarn needle
Scissors
Small wooden dowel or a toothpick (optional, for the trunk)
Hot glue gun (if using a wooden dowel)
Abbreviations:

ch: chain
st: stitch
sc: single crochet
hdc: half double crochet
dc: double crochet
sl st: slip stitch
Pattern:

Tree:
Start with green yarn.

Magic ring, 6 sc into the ring. (6 stitches)
Inc in each st around. (12 stitches)
Sc, inc around. (18 stitches)
Sc 2, inc around. (24 stitches)
Sc 3, inc around. (30 stitches)
Sc 4, inc around. (36 stitches)
Sc 5, inc around. (42 stitches)
Sc 6, inc around. (48 stitches)
Sc 7, inc around. (54 stitches)
Sc in each st around. (54 stitches)
Sc 7, dec around. (48 stitches)
Sc in each st around. (48 stitches)
Sc 6, dec around. (42 stitches)
Sc in each st around. (42 stitches)
Sc 5, dec around. (36 stitches)
Sc in each st around. (36 stitches)
Sc 4, dec around. (30 stitches)
Sc in each st around. (30 stitches)
Sc 3, dec around. (24 stitches)
Sc in each st around. (24 stitches)
Sc 2, dec around. (18 stitches)
Sc in each st around. (18 stitches)
Sc, dec around. (12 stitches)
Stuff the tree firmly with fiberfill or stuffing.
Dec around. (6 stitches)
Fasten off and leave a long tail for sewing.
Decorations:
You can use various colors of yarn to create decorative elements on the tree. Here are some simple ideas:

Balls:
Using various colors:

Magic ring, 6 sc into the ring. (6 stitches)
Sl st into the first sc to close the round.
Fasten off and leave a long tail for sewing. Make several balls in different colors.
Garland:
Using a contrasting color (optional):

Ch 30 (or any desired length).
Starting from the second ch from the hook, sl st in each ch across.
Fasten off and leave a long tail for sewing.

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