B-Tree Insert and In-Order Traversal in Python

class BTreeNode:
    def __init__(self, leaf=False):
        self.leaf = leaf
        self.keys = []
        self.children = []

    def is_full(self, t):
        return len(self.keys) == 2 * t - 1


class BTree:
    def __init__(self, t=2):
        self.t = t
        self.root = BTreeNode(leaf=True)

    def insert(self, key):
        if self.root.is_full(self.t):
            new_root = BTreeNode(leaf=False)
            new_root.children.append(self.root)
            self._split_child(new_root, 0)
            self.root = new_root
        self._insert_non_full(self.root, key)

    def _split_child(self, parent, i):
        t = self.t
        child = parent.children[i]
        new_child = BTreeNode(leaf=child.leaf)
        parent.keys.insert(i, child.keys[t - 1])
        parent.children.insert(i + 1, new_child)
        new_child.keys = child.keys[t:]
        child.keys = child.keys[:t - 1]
        if not child.leaf:
            new_child.children = child.children[t:]
            child.children = child.children[:t]

    def _insert_non_full(self, node, key):
        if node.leaf:
            i = 0
            while i < len(node.keys) and key > node.keys[i]:
                i += 1
            node.keys.insert(i, key)
        else:
            i = 0
            while i < len(node.keys) and key > node.keys[i]:
                i += 1
            if node.children[i].is_full(self.t):
                self._split_child(node, i)
                if key > node.keys[i]:
                    i += 1
            self._insert_non_full(node.children[i], key)

    def to_list(self):
        result = []

        def traverse(node):
            if node.leaf:
                result.extend(node.keys)
            else:
                for i in range(len(node.keys)):
                    traverse(node.children[i])
                    result.append(node.keys[i])
                traverse(node.children[-1])

        traverse(self.root)
        return result


if __name__ == "__main__":
    tree = BTree(t=2)
    for value in [10, 20, 5, 6, 12, 30, 7, 17]:
        tree.insert(value)
    print(tree.to_list())