Each tree is made of binary splits. What this is and how you make one from scratch is shown here and here (fastai tutorial). A decision Tree is basically a series of binary splits.
<aside> 💡 Great advantage → not much preprocessing to do, as explained here! Therefore hard to mess it up. A good starting point for tabular data. Create a Baseline Model
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Post-pruning to maximize accuracy of Decision Trees
Video
https://www.youtube.com/watch?v=_L39rN6gz7Y&ab_channel=StatQuestwithJoshStarmer