SOURCE

const chainData = [
    { 
        deptId: '1', deptName: 'A部门',
        chains: [
            { chainId: '12', chainName: 'A部门-供应链1' },
            { chainId: '13', chainName: 'A部门-供应链2' }
            ] 
     }
    ];


const handleChainData = chainData.map(item => {
    const children = [];
    item.chains.forEach(chainItem => {
        children.push({
            value: chainItem.chainId,
            label: chainItem.chainName,
        });
    });
    return {
        value: item.deptId,
        label: item.deptName,
        children,
    };
});

console.log(JSON.stringify(handleChainData));