Just copy the struct and create the simple methods for creating the children nodes.

Something like this:

struct Node {
    value: u32,
    left: Option<Box<Node>>,
    right: Option<Box<Node>>,
}

impl Node {
    fn new(value: u32) -> Self {
        Node {
            value,
            left: None,
            right: None,
        }
    }

    fn left(mut self, node: Node) -> Node {
        self.left = Some(Box::new(node));
        self
    }

    fn right(mut self, node: Node) -> Node {
        self.right = Some(Box::new(node));

        self
    }
}

You must return the result, not print it.