const tree = {
    name: 'root',
    children: [
        { name: '叶子1-1' },
        { name: '叶子1-2' },
        {
            name: '叶子2-1',
            children: [{
                name: '叶子3-1',
                children: [{
                    name: '叶子4-1',
                    children: [{}]
                }]
            }]
        }
    ]
}

function getLevel(tree) {
    if (tree == null) return 0;
    const queue = [tree]
    let dep = 0;
    while (queue.length) {
        dep++;
        const size = queue.length
        for (let i = 0; i < size; i++) {
            const node = queue.shift()
            if (node.children) {
                for (const child of node.children) {
                    queue.push(child)
                }
            }
        }
    }
    return dep
}
console.log(getLevel(tree));