How to add nodes in bulk using RestAPI?

The REST API doesn't permit 'bulk imports' So whilst the suggestions buy Tiziano and Youseff are correct, you would need to repeat the process as REST API uses an imperative model - think of it as multiple remote tmsh commands that need to be executed in a given order.

The easiest way to bulk import would be to consider Ansible, whilst the SDK under the hood will send multiple commands - it appears more declarative in nature.

---
- name: Setup
  hosts: f5
  connection: local
  gather_facts: True

  vars:
    f5Provider:
      server: "{{inventory_hostname}}"
      user: "{{f5User}}"
      password: "{{f5Pass}}"
      validate_certs: no
      transport: rest
    nodelist:
      - {name: 'test01', address: '8.8.8.8', priority_group: 1, state: 'present'}
      - {name: 'test02', address: '8.8.4.4', priority_group: 1, state: 'present'}

  environment:
      F5_SERVER: "{{ inventory_hostname }}"
      F5_USER: "{{ f5Provider.user }}"
      F5_PASSWORD: "{{ f5Provider.password }}"
      F5_VALIDATE_CERTS: "{{ f5Provider.validate_certs }}"
      F5_SERVER_PORT: "{{ f5Provider.server_port }}"

  tasks:
    - name: Add pool 'test_pool'
      bigip_pool:
        lb_method: least-connections-member
        name: test_pool
        monitor_type: single
        monitors:
          - /Common/gateway_icmp
        priority_group_activation: 0
      delegate_to: localhost
      notify: Save configuration

    - name: Add nodes
      bigip_node:
        address: "{{ item.address }}"
        name: "{{ item.name }}"
      loop: "{{ nodelist }}"
      delegate_to: localhost
      notify: Save configuration

    - name: Add pool members to Pool 'test_pool'
      bigip_pool_member:
        pool: test_pool
        address: "{{ item.address }}"
        name: "{{ item.name }}"
        port: 53
        priority_group: "{{ item.priority_group }}"
        state: "{{ item.state }}"
      loop: "{{ nodelist }}"
      delegate_to: localhost
      notify: Save configuration