SK_LightningTreeApp.app

<aura:application extends="force:slds">
    <c:SK_LightningTreeCmp ltngcurrentRecId="0019000000ld4kO"
          ltngSobjectname="Account"
          ltngParentFieldAPIName="ParentId"
          ltngLabelFieldAPIName="Name"
          ltngHierarchyHeader="Account Hierarchy"/>
    
    
    <c:SK_LightningTreeCmp ltngcurrentRecId="5009000000GJkJG"
          ltngSobjectname="Case"
          ltngParentFieldAPIName="ParentId"
          ltngLabelFieldAPIName="CaseNumber"
          ltngHierarchyHeader="Case Hierarchy"/>
</aura:application>

SK_LightningTreeCmp.cmp

<aura:component controller="SK_LightningTreeCmpController">
    <aura:attribute name="ltngcurrentRecId" type="String" required="true"/>
    <aura:attribute name="ltngSobjectname" type="String" required="true"/>
    <aura:attribute name="ltngParentFieldAPIName" type="String" required="true"/>
    <aura:attribute name="ltngLabelFieldAPIName" type="String" required="true"/>
    <aura:attribute name="ltngHierarchyHeader" type="String" required="true"/>
    <aura:attribute name="items" type="Object"/>
    
    <aura:handler event="aura:waiting" action="{!c.showSpinner}"/>
    <aura:handler event="aura:doneWaiting" action="{!c.hideSpinner}"/>
    <div class="slds-align--absolute-center">
        <lightning:spinner aura:id="spinner" variant="brand" size="large" class="slds=hide"/>
    </div>
    <aura:handler name="init" value="{!this}" action="{!c.doInit}" />
    <lightning:tree items="{!v.items }" header="{!v.ltngHierarchyHeader}" onselect="{!c.handleSelect}"/>
</aura:component>

SK_LightningTreeCmpController.cls

public class SK_LightningTreeCmpController {
	@AuraEnabled
    public static List<HierarchyData> findHierarchyData(string recId, string sObjectName, string parentFieldAPIname, string labelFieldAPIName){
        List<HierarchyData> returnValue = new List<HierarchyData>();
        string queryString = 'select id, '+labelFieldAPIName+ ' ,' +parentFieldAPIname+ ' from '+sObjectName;
        //Section to get all child account details from ultimate parent starts-------------------------
        List<String> currentParent      = new List<String>{};
        Integer level               = 0;
        Boolean endOfStructure      = false;
        //method to find ultimate parent of account
        string topMostparent = GetUltimateParentId(recId, sObjectName,parentFieldAPIname );
        currentParent.add(topMostparent);
        system.debug('**********topMostparent:'+ currentParent);
        //Loop though all children
        string finalQueryString = '';
        List<sObject> queryOutput = new List<sObject>();
        while ( !endOfStructure ){  
            if( level == 0 ){
                finalQueryString = queryString + ' where id IN : CurrentParent ORDER BY '+parentFieldAPIname +'  Limit 1000';
            } 
            else {
                finalQueryString = queryString + ' where ParentID IN : CurrentParent ORDER BY '+parentFieldAPIname+' Limit 1000';
            }
            system.debug('********finalQueryString:'+finalQueryString);
            if(finalQueryString != null && finalQueryString !=''){
                try{
                    if(Limits.getLimitQueries()-Limits.getQueries()>0){
                        queryOutput = database.query(finalQueryString);
                    }else{
                        endOfStructure = true;
                    }
                }catch(exception ex){ 
                    endOfStructure = true;
                }
            }
            if( queryOutput.size() == 0 ){
                endOfStructure = true;
            }
            else{
                currentParent.clear();
                //iterating through query output
                for ( Integer i = 0 ; i < queryOutput.size(); i++ ){
                    sobject sb= queryOutput[i];
                    currentParent.add(string.valueof(sb.get('id')) );
                    HierarchyData ss = new HierarchyData();
                    if(sb.get('id') == recId || level == 0){
                        ss.expanded = true;
                    }else{
                        ss.expanded = false;
                    }
                    ss.rec = sb;
                    returnValue.add(ss);
                 }
            }
            level++;
        }
        system.debug('**********returnValue:'+returnValue);
        return returnValue;
    }
    
	// Find the tom most element in Heirarchy  
    // @return objId
    public static String GetUltimateParentId( string recId, string sObjectName, string parentFieldAPIname ){
        Boolean top = false;
        while ( !top ) {
            string queryString = 'select id , ' +parentFieldAPIname+ ' from '+sObjectName + ' where Id =:recId LIMIT 1';
            system.debug('**********queryString GetUltimateParentId:'+queryString);
            sobject sb = database.query(queryString);
            
            if ( sb.get(parentFieldAPIname) != null ) {
                recId = string.valueof(sb.get(parentFieldAPIname));
            }else {
                top = true;
            }
        }
        return recId ;
    }

    public class HierarchyData{
        @AuraEnabled
        public sObject rec{get;set;}
        @AuraEnabled
        public boolean expanded{get;set;}
        public HierarchyData(){
            expanded = false;
        }
    }
}

SK_LightningTreeCmpController.js

({
    doInit: function (component, event, helper) { 
        console.log('doInit of component called');
        var trecid = component.get('v.ltngcurrentRecId');
        var tsObjectName= component.get('v.ltngSobjectname');
        var tparentFieldAPIname= component.get('v.ltngParentFieldAPIName');
        var tlabelFieldAPIName= component.get('v.ltngLabelFieldAPIName');
        helper.callToServer(
            component,
            "c.findHierarchyData",
            function(response) {
                var apexResponse = response;
                var roles = {};
                console.log('*******apexResponse:'+JSON.stringify(apexResponse));
                var results = apexResponse;
                
                roles[undefined] = { Name: "Root", items: [] };
                
                apexResponse.forEach(function(v) {
                    //var sk = v.rec;
                    //var labelValue= sk[tlabelFieldAPIName];
                    roles[v.rec.Id] = { 
                        label: v.rec[tlabelFieldAPIName] ,
                        name: v.rec.Id, 
                        expanded:v.expanded,
                        items: [] };
                });
                console.log('*******roles:'+JSON.stringify(roles));
                apexResponse.forEach(function(v) {
                    roles[v.rec[tparentFieldAPIname]].items.push(roles[v.rec.Id]);   
                });                
                component.set("v.items", roles[undefined].items);
                console.log('*******roles[undefined].items:'+JSON.stringify(roles[undefined].items));
            }, 
            {
                recId: component.get('v.ltngcurrentRecId'),
                sObjectName: component.get('v.ltngSobjectname'),
                parentFieldAPIname: component.get('v.ltngParentFieldAPIName'),
                labelFieldAPIName: component.get('v.ltngLabelFieldAPIName')
            }
        );
        
    },
    showSpinner: function(component, event, helper) {
        var spinner = component.find("spinner");
        $A.util.removeClass(spinner, "slds-hide");
    },
    hideSpinner: function(component, event, helper) {
        var spinner = component.find("spinner");
        $A.util.addClass(spinner, "slds-hide");
    },
    handleSelect: function (cmp, event, helper) {
        //return name of selected tree item
        var myName = event.getParam('name');
        alert("You selected: " + myName);
    }
})

SK_LightningTreeCmpHelper.js

({
	callToServer : function(component, method, callback, params) {
        console.log('Calling helper callToServer function');
		var action = component.get(method);
        if(params){
            action.setParams(params);
        }
        console.log(JSON.stringify(params));
        action.setCallback(this, function(response) {
            var state = response.getState();
            if (state === "SUCCESS") {
                //alert('Processed successfully at server');
                callback.call(this,response.getReturnValue());
            }else if(state === "ERROR"){
                alert('Problem with connection. Please try again.');
            }
        });
		$A.enqueueAction(action);
    }
})

Small edit for SK_LightningTreeCmpController.cls line
finalQueryString = queryString + ' where ' + parentFieldAPIname + ' IN : CurrentParent ORDER BY '+parentFieldAPIname+' Limit 1000';
This will allow the component to be used for additional objects other than the Account.

Two questions, too, if that is ok. Is there any way to add in additional fields with the Name? Something as simple as the record type would be super helpful. And also, is there any way to create a tree that all originate from a different object?

Is there a sample TestClass for the Apex controller?